Circuit switched private communication network with integrated packet switched multimedia extensions

ABSTRACT

A multimedia data network (MMN) operating according to a packet switched standard and a circuit switched network (TABX) are connected without a gateway (GW). The circuit switched network (PABX) comprises a multimedia controller (MMC) which receives signaling messages from multimedia terminals (MT) and controls the switching resources (SW) of the circuit switched network (PABX) on the basis of these signaling messages during a call set-up. The multimedia controller (MMC) makes the multimedia terminals (MT) normal extensions of the extension space of the circuit switched network (PABX). Therefore, multimedia terminals (MT) and normal telephony terminals (TT) can perform a data exchange through the switching resources (SW) controlled by the multimedia controller. Additionally, the multimedia controller (MMC) can provide supplementary services of the circuit switched network to the multimedia terminal (MT). It is also possible that the multimedia controller (MMC) performs a network resource management of resources in the multimedia data network (MMN). Thus, the multimedia controller (MMC) provides a full integration of the multimedia terminals (MT) into the circuit switched network without using the functionality of protocol conversion of a gateway (GW).

This application is the U.S. national phase of international applicationPCT/EP01/00970 filed Jan. 30, 2001, which designated the U.S. and claimspriority of DE 100 05 282.7 filed Feb. 7, 2000, the entire contents ofeach of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a circuit switched privatecommunication network for providing communications between one or morefirst subscriber stations of the private communication network and oneor more second subscriber stations of a packet switched privatemultimedia data network without using a gateway there between. Theinvention also relates to a method for providing communications betweenthe circuit switched private communication network and the packetswitched private multimedia data network.

In particular, the invention addresses the problem of how multimediaterminals of a multimedia data network can be made part of the extensionspace of a private circuit switched communication network, e.g. aprivate branch exchange system PABX. Therefore, the invention isgenerally directed to a PABX system with integrated multimediaextensions wherein data network infrastructure is used to make themultimedia terminals accessible and access the private network. Morespecifically, the gateway for converting the data communication from thetelephony protocols used on the circuit switched network side tosignaling and multimedia protocols used on the data network side shouldbe avoided.

BACKGROUND OF THE INVENTION

The availability of voice over packet network technology and inparticular, although not exclusively, corporate multimedia network,circuit switched and packet switched network technology has providedusers with new services and functionalities which had not been availablein the conventional telephony technologies. For example, the Internet orother private packet switched networks (multimedia data networks) orInternet-based multimedia communication technologies do not only offeradvanced speech processing but also audio, video and/or other moreadvanced data communication services.

Due to the intrinsic packet switched nature, products for allowing theintegration of these new Internet-based multimedia communicationtechnologies with the older but more widespread and well-knowntraditional circuit switched telephony technologies are necessary. Sincethere is an exponential growth of the Internet and therefore of themultimedia data networks that support it, the number of potentialcustomers for Internet-based multimedia communication systems increasesevery day. However, of course these customers still want to have accessto the traditional circuit switched telephony systems, e.g. to a privatebranch exchange system PABX or generally to a circuit switched privatecommunication network (PCN).

Each “world”, namely the circuit switched technology and the packetswitched technology, must be interfaced as regards the usage of theirprotocols for signaling and communication in order to allow acommunication between these two apparently so different “worlds”.

The two “worlds” are indeed completely different regarding the call setup and the call routing and other functionalities. Whilst in a circuitswitched network PABX the first subscriber stations TT set up callsbetween each other by simply dialing the directory number whilst theswitching means SW will connect the call, multimedia terminals MT beingbased on a packet switched technology operate completely differently. Ina multimedia data network the multimedia terminals have transportaddresses, identifications like an e-mail address, a URL, user nameetc., an authentication (password) and have specific capabilities likeaudio, video, data, or multiconference functionalities. Conventionally,in a multimedia data network the multimedia terminals MT can have a“freeseating feature”, e.g. they can be connected to the multimedia datanetwork at arbitrary connectors. In the multimedia data network themultimedia terminals MT perform a registration procedure which makesthem known within the multimedia data network. All such features areintrinsically different to the circuit-switched technology intraditional private branch exchange systems PABX.

PRIOR ART SOLUTIONS

FIG. 1 of the attached drawings shows a typical block diagram of acommunication system where intercommunication between Internet-basedmultimedia communication systems and traditional telephony systems ispossible. A circuit switched private communication network, i.e. aprivate branch exchange PABX, including a switching means (switchingresources) SW and a multimedia data network (packet switched multimediadata network) each has first subscriber stations TT and secondsubscriber stations MT (TT: telephony terminal; MT: multimediaterminal). As is well known, typical protocols used for datacommunication within a multimedia data network comprise such protocolsas H.323, SIP, TCP/IP, IPX and others. Typically, the controller withinthe multimedia data network serving a plurality of second subscriberstations MT is a gatekeeper GK schematically shown in FIG. 1. On theother hand, the traditional telephony system PABX being intrinsically ofa circuit-switched nature uses such conventional protocols andcommunication techniques as defined in the signaling system 7 (SS7),ISDN or PCM modulation techniques.

Typically in 99% of all cases a gateway GW acts as an interface forconverting the communications received from one side to the protocols orthe signaling techniques available on the other side. Thus, the gatewaysconvert from the signaling and media protocols used in the data networkside to one or more telephone protocols used in the circuit-switchednetwork side.

FIG. 1 only shows one example of the interconnection of the packetswitched and circuit switched networks. Typically, in a corporatenetwork it is quite common to connect the gateways providingintercommunication with multimedia data networks to the PABX of thecompany in order to provide a communication between the subscriberstations TT, MT of both systems.

Furthermore, there are systems where the gateway GW is not providedbetween the two networks PABX, MMN but where the gateway GW is actuallyincorporated as part of the branch exchange system PABX. However, thefunctionality is quite the same, namely to perform a protocol conversionbetween the differently used protocols.

U.S. Pat. No. 5,181,199 describes a packet switching system, moreprecisely a private branch exchange having a comparatively small numberof ISDN circuits. In a circuit interface a table is provided for thepurpose of conversion between a logical channel lying between ISDNterminal equipment and the private branch exchange and one lying betweenthe private branch exchange and an ISDN network. The system is entirelybased on circuit switching technology in which packets of the D channelcontain signaling information and can be used for controlling theswitching resources of the circuit switched system. The document onlyrelates to providing circuit switched connections between individualISDN terminals.

The preamble of claim 1 relates to a standard PABX comprising switchingresources for providing communications between first subscriber stationsbelonging to the circuit switched extension realm of the system.

SUMMARY OF THE INVENTION

As explained above, whilst the multimedia terminals MT intrinsicallyindependently of the specific type of multimedia data network MMN havesome common features like the usage of a transport address, packetswitched data communication, the identification etc., they can only bereached from the circuit switched network, e.g. a private branchexchange PABX, if they are interconnected by a gateway GW. That is, themultimedia terminals MT can communicate with the telephony terminals TT,however, whenever a new type of multimedia data network is to beconnected there is the need to provide a new gateway GW which adds tothe cost of the system. Furthermore, the solution is quite cumbersome,because the multimedia terminals MT can only be connected to connectorsof the multimedia data network, i.e. they cannot—without the usage of agateway—be plugged directly into a connector of the circuit-switchednetwork PABX. That is, the multimedia terminals MT are not integratedinto the circuit-switched network.

Therefore, the object of the present invention is to provide acircuit-switched private communication network for providingcommunications between its subscriber stations and multimedia subscriberstations of packet-switched networks without the usage of a gateway forestablishing intercommunication. That is, the object of the presentinvention is to provide a complete integration between the traditionaltelephony system and the new Internet-based multimedia communicationsystems, in the scope of private and business communication networks.The invention is to provide a seamless integration of privatecommunication networks based on circuit-switched equipment with privatemultimedia networks based on packet-switched equipment.

SOLUTION OF THE INVENTION

This object is solved by a circuit switched Private CommunicationNetwork system in accordance with claim 1.

According to one aspect of the invention the circuit-switched privatecommunication network comprises a controller for controlling the use ofthe switching resources of the circuit-switched private communicationnetwork for setting up calls between the telephony terminals and/or themultimedia terminals on the basis of signaling information received atleast from a second subscriber station (multimedia terminal) during acall set-up. That is, the controller according to the invention caninterpret the signaling from the multimedia terminal and can control theswitching resources in accordance with the interpreted content of thereceived signaling information. Since the controller can interpret atleast the signaling information and since the circuit-switched privatecommunication network is aware of the capabilities, categories,identities etc. of the multimedia terminals and is also aware of thekind of equipment it is connected to on the data network side, it canactually control the usage and seizure of switching resources in thecircuit-switched private communication network without the use of aprotocol conversion. However, if necessary even a gateway could betreated as one of the multimedia extensions of the circuit-switchednetwork if it is previously registered in the controller.

Therefore, according to a second aspect of the invention any multimediaterminal undergoes a registration procedure in the controller of theinventive circuit-switched private communication network such that whena corresponding signaling information is received from a registeredmultimedia terminal the controller can act correspondingly.

Since the multimedia terminals are not invisible any more from thecircuit-switched private communication network's point of view anytelephony service available for PABX terminals will also be availablefor multimedia terminals. This also includes all services provided toPABX extensions but not accessible to external users connected to thePABX through public/private trunk lines.

Furthermore, all the logging and metering functions provided by the PABXare available for the multimedia terminals. According to the inventioncalls to/from the multimedia terminals are now regarded as normalinternal calls in a circuit-switched network. Complete individualcharging can be done for the multimedia terminals and detailed callinformation logging of the calls made and received by the multimediaterminals can be performed. Furthermore, advanced value added servicescan be provided to the multimedia terminals, like freeseating (makingavailable the freeseating function already existing in the PABX also forthe MT terminals) and access to the PABX messaging system.

Additionally, other advantages that deliver cost savings and improvedperformance are obtained with the invention here described. Suchadvantages are: it is now an easy task to keep the numbering spaceconsistent, since there are not different number series initiated ineach system (the PABX and the Gateway). All the Operations & Managementfunctions provided by the PABX for its extensions is available for theMTs. MTs can be managed just as any other kind of PABX's extensions,instead of doing it from the Gateway, with the Gateway's own O&Minterface and Management System. This means that only one instead of twodifferent systems has to be managed. For the system that results from animplementation of the here described invention, the QoS measured interms of unavailability is, at worst, the square root of that same QoSof the system composed of PABX and Gateway (assuming thatunavailability(Gateway>unavailability(PABX)). This means that theservice level offered by an implementation of the here describedinvention is much higher than that of a couple PABX plus Gateway.

According to the invention the controller does not perform a protocoladaption but intrinsically has a layer structure similar to the OSI(OSI: open system interconnection) structure necessary for extractingthe signaling information from messages received from multimediaterminals. That is, according to the invention the physical signalinginformation received from multimedia terminals is processed in the layerstructure of the controller in a similar manner as would be done e.g. ina gatekeeper of the multimedia data network. Thus, the input to thecontroller are physical signaling messages (signals) which areinterpreted and the output of the controller directed to the switchingmeans of the circuit-switched network are again physical signalsadjusted in accordance with the interpreted content of the signalinginformation. Precisely for achieving this interpretation the controlleraccording to the invention has a layer structure similar to the OSIlayer structure conventionally provided in the multimedia data network.Therefore, there is not need to employ a gateway for performing acomplete signal or protocol conversion.

Further advantageous embodiments and improvements of the invention canbe taken from the dependent claims. Furthermore, it should be noted thaton the basis of the teachings enclosed herein various modifications andvariations of the invention can be carried out. In particular, theinvention comprises embodiments consisting of features which have beenseparately described in the specification and/or claimed in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 basically illustrates the layout of conventional solutions forproviding an intercommunication between a circuit-switched network and apacket-switched network using a gateway GW for protocol conversion;

FIG. 2 shows a block diagram of a communication system where amultimedia data network is connected to a private branch exchange PABXwithout the use of a gateway GW whilst the PABX according to theinvention comprises an inventive controller MMC (multimedia controller);

FIG. 3 shows a similar block diagram as in FIG. 2, where the multimediaterminals MT are directly plugged into the private branch exchange PABX;

FIG. 4 shows a block diagram of the multimedia controller MMC accordingto the invention in terms of a layer structure;

FIG. 5 shows an example of the access layer part an OSI layer structureof a multimedia terminal operating in the multimedia data networkaccording to the structure mapping of the present invention;

FIG. 6 shows a functional block diagram of the physical and data-linksub-layer means PDLSUB of the access layer means ALM (an access printedcircuit board PCB) which provides the physical connection between thedata network or a multimedia terminal and the private branch exchange;

FIG. 7 shows a functional block diagram of the network and transportsub-layer means NTSUB of the access layer means ALM implementing thecommunication between the network hardware HW and the application layerAL;

FIG. 8 shows a functional block diagram of the protocol handling layermeans PHM taking care of uniform syntax and semantics of the messages ofthe multimedia protocol being used;

FIG. 9 a shows a functional block diagram of the media handling layermeans MHL allowing the transcoding, packetization and framing ofreal-time information streams;

FIG. 9 b shows a functional block diagram of the media gateway means MGMshown in FIG. 9 a responsible for the transcoding of real-timeinformation streams;

FIG. 10 shows a functional block diagram of the basic services means DSMand the supplementary services means SSM of the application layer ALwhich directly interfaces with the PABX's core layer COL;

FIG. 11 shows a functional block of the operations O & M operation andmaintenance layer means OML;

FIG. 12 shows a flow chart for making a multimedia terminal MT part ofthe PABX extension space, i.e. for integrating the multimedia terminalMT in a seamless manner into the circuit-switched private communicationnetwork;

FIG. 13 a shows a diagram of a discovery signaling and a discoveryrequest message processing algorithm which allow the circuit-switchedprivate communication network to reveal itself to a given multimediaterminal;

FIG. 13 b shows a diagram of a registration signaling and a registrationrequest message processing algorithm illustrating the registrationprocedure of the multimedia terminal MT in the circuit-switched networkPABX, in particular the possibilities of the PABX to take a decisionabout admission or rejection of a multimedia terminal MT within the PABXextension space;

FIG. 13 c shows a flow chart of an identity check procedure (carried outin step ST13 b 2 in FIG. 13 b), which allows PABX to check the identityof a multimedia terminal MT, in particular checking the e-mail address,the ULR and the E.164 directory number;

FIG. 14 illustrates a diagram of a switching resources seizing algorithmwhere the PABX decides whether internal switching resources of the PABXshould be used for a type of a communication between the subscriberstations;

FIG. 15 a illustrates the sending of messages internally in the PABX forsetting up a new call between two multimedia terminals MTA, MTB for aPABX with a distributed architecture;

FIG. 15 b shows a flow chart illustrating the decision process whensending messages in FIG. 15 a for setting up a call between twomultimedia terminals MTA, MTB, in particular to decide the mediatransmission path to use for the communication and also to instruct agiven multimedia terminal to uses the set-up path subsequently;

FIG. 15 c a call setup diagram similar to FIG. 15 a where ALA and ALBare merged into one application layer ALA for a PABX having anone-distributed centralized architecture;

FIG. 15 d a diagram for a flow chart similar to FIG. 15 b for thenone-distributed architecture PABX of FIG. 15 c, in particular thesource and destination transport address selection;

FIG. 16 shows the procedure when the PABX and a given multimediaterminal MT exchange each other's transport addresses used to exchange aspecial signaling related to the use of supplementary services;

FIG. 17 shows a algorithm for a network resources management whichallows the PABX to determine signaling whether network resources areavailable for carrying out a given communication;

FIG. 18 shows a use example with a H.323 Gatekeeper/Gateway applicationintegrated into a PABX, in particular the architecture of the layerimplementation;

FIG. 19 a signaling diagram where the multimedia terminal MT on the leftis performing a discovery and a registration procedure and where themultimedia terminal on the right is performing a registration procedureonly, also showing a part of the call setup procedure between the twomultimedia terminals MTs;

FIG. 20 shows a continuation of the call setup signaling of FIG. 19; and

FIG. 21 shows a call release procedure for the call setup in accordancewith FIGS. 19–20.

In the drawings the same or similar reference numerals denote the sameor similar parts throughout.

Before coming to a detailed discussion of the invention it should benoted that in the description of the embodiments of the inventionhereinafter special examples of signaling messages and protocols likeH.323, SIP, TCP/IP, IPX, H.225.0, RAS, H.245, H.225.0/Q.931 and H.323are described for illustrating the inventive concept. Furthermore, theoperation of the inventive controller is described with reference to alayer model (similar as in the OSI structure). However, it should benoted that these descriptions are by no means limiting for the inventionand similar functionalities and messages can be found in othermultimedia data networks specifications.

Therefore, what has been described below is only what the inventorspresently conceive as the best mode of the invention which shouldhowever not be taken as limiting the invention in any way.

PRINCIPLE OF THE INVENTION

Hereinafter, the principle of the invention will be described. FIG. 2and FIG. 3 show the basic set-up of the communication system accordingto the invention. As shown in FIG. 2, the multimedia data network MMNhas a plurality of second subscriber stations MT (hereinafter calledmultimedia terminals) and the multimedia data network MMN is connectedvia a communication connection KL using e.g. a H.323 protocol forsignaling and data exchange to the circuit-switched privatecommunication network PABX having one or more fist subscriber stationsTT (hereinafter also referred to as the telephony terminals TT). Thecircuit-switched private communication network PABX comprises switchingresources or a switching means SW for providing switchingfunctionalities between the subscriber stations. As shown in FIG. 3,there is no actual need to go through the multimedia data network MMNitself because the multimedia terminals MT according to the inventioncan be directly connected to the circuit-switched network PABX.

According to the invention there is neither a gateway functionalitybetween the networks in FIG. 2 nor is there a gateway incorporated inthe circuit-switched network in FIG. 3. Instead, the PABX networkcomprises a controller MMC (hereinafter also referred to as a multimediacontroller) which controls the use of switching resources SW of thecircuit-switched private communication network PABX for setting up callsbetween said first and/or said second subscriber stations TT, MT on thebasis of some interpreted signaling information received at least fromthe second subscriber station MT during a call set-up.

As explained before, the multimedia terminals MT operate according to acompletely different packet-switched technology whilst thecircuit-switched network PABX operates according to a circuit-switchedtechnology. However, the multimedia controller MMC according toinvention can understand the signaling information—which still has thepacket network protocol format and—and it can decode this signalinginformation in order to control the seizure of switching resources inthe private network PABX based on the interpreted content of thesignaling information.

Of course, the multimedia controller can also receive signalinginformation from other entities in the communication network, e.g. fromthe telephony terminals TT in order to set-up a call to the multimediaterminal MT. However, the point of the present invention is that thecontroller will understand signaling information having a completelydifferent (packet-switched network) format and that there is no need toprovide a gateway for a protocol conversion as in FIG. 1.

This understanding of the signaling information from the multimediaterminal MT requires that the multimedia terminal MT is part of the PABXextension space and that the controller at least partly reflects the OSIlayer structure of the protocol used in the data network to which themultimedia terminal MT belongs. This recognition or registration ofmultimedia terminals MT which is a prerequisite for carrying out theinvention will be explained below with further details referring to theembodiments of the invention.

Due to registration and discovery procedures according to the inventionthe multimedia terminals MT are not “invisible” any longer from thecontroller's or PABX's point of view. The PABX can decode the signalinginformation because it is now aware of the capabilities, categories,identities etc. of the (registered) multimedia terminals MT. The PABX isalso aware of the kind of equipment it is connected to on the datanetwork side (a gateway, a multimedia terminal MT, a multi-conferenceunit MCU etc.). Thus, multimedia terminals can be managed just as anyother kind of PABX extension instead of using a gateway. This means,that only one instead of two different systems must be managed in aunified manner.

It should also be noted that the multimedia controller according to theinvention comprises a general set-up of layer means (realized inhardware or software) which are so generic that they allow to providecommunications with any type of multimedia terminal using differentprotocols as long as some of the entities in the layer means are adaptedto these protocols. This will be explained hereinafter.

First Embodiment (Controller Layer Architecture)

The multimedia controller MMC shown in FIGS. 2, 3 according to theinvention allows to make the multimedia terminals MT an integral part ofthe PABX's extension space. That is, from the PABX's point of view themultimedia terminals MT are a type of extension just like the telephonyterminals TT. In order to do so the multimedia controller MMC has somespecial functionalities which are expressed in a 5-layer architecture.Essentially this layer architecture of the controller transforms thePABX into an integrated multimedia communication system. By doing so, itnot only gets rid of the usage of gateways GW (which can however beagain considered as normal extension of the PABX) but it also allows tooffer new functionalities and supplementary services to the multimediaterminals MT from the circuit-switched network PABX which have so farnot been available for the multimedia terminals MT.

As shown in FIG. 4 the multimedia controller MMC layer structure mirrorspartly a layer structure as used in some of the protocols available inthe multimedia data networks. It should be noted that here no referencesto the OSI model are made. The OSI model is a framework which can befollowed or not by implementations and in the present invention a layerstructure is used but not one which directly follows OSI. The Accesslayer matches layers 1 to 4 of the OSI model, but the similarities endup there. Concretely, there are no session and presentation layers, andthe Application layer described here according to the invention is quitefar away from the OSI model's concept of “Application layer”.

In particular, an access layer means ALM comprises a physical and datalink sub-layer PDLSUB and a network and transport sub-layer NTSUB. Inaddition to the access layer means ALM there is protocol handling layermeans PHLM, a media handling layer means MHL, an application layer ALcomprising basic services BSM and supplementary services SSM, anoperation and maintenance layer means OML and the PABX's core layer COLessentially comprising the physical switching resources SW as shown inFIGS. 1–3. At the very bottom in FIG. 4 the physical data networkconnection, e.g. through the communication link KL is shown.

These layers and special procedures as described hereinafter arenecessary to make the multimedia terminal MT a real extension of thePABX's extension space. Thus a complete seamless integration of themultimedia terminals MT of any kind into the PABX is possible.

It should be noted that in the description of the layer architecturehereinafter the layer designations are selected to correspond to some ofthe well-known expressions used in other protocols. However, theseexpression should not be limited to the specific layers in theseprotocols and corresponding functionalities can be identified in otherprotocols not specifically listed here.

Access Layer

The access layer means ALM of the multimedia controller MMC is necessaryto interconnect the data network MMN (or respectively the multimediaterminal MT) and the multimedia controller MMC. As shown in FIG. 5,typically a multimedia terminal MT operating in the multimedia networkor in fact the multimedia data network itself operates according to adata network protocol stack consisting of a physical and data linksub-layer PDLSUB and a network and transport sub-layer NTSUB. In orderto allow the multimedia terminals MT of the data network to set-up dataconnections in the PABX the multimedia controller MMC of the PABX mustmirror such a data network protocol stack of the access layer in themultimedia data network. Therefore, using the OSI layer implementation(OSI: open system interconnection) the access layer means ALM of themultimedia controller MMC according to the invention must implementthese two sub-layers PDLSUB, NTSUB.

In the access layer all data network related issues are contained suchthat no changes to the upper two layers OML, PHLM, MHL; AL, BSM, SSM arenecessary even if for example a TCP/IP adapted access layer would bereplaced by an IPX access layer because the multimedia terminals MT tobe integrated are operating according the IPX protocol. However, as willbe seen below, even the generic access layer devices do not operate asif they were a gateway. That is, although some type of conversion andadaption is necessary in the access layer ALM, the access layer is onlyprovided to attract, interpret and decode the signaling messages of therespective protocols. Therefore, by no means can the access layer becompared with the functionality of a gateway.

Physical and Data Link Sub-layer

FIG. 6 shows a functional block diagram of the physical and data linksub-layer PDLSUB. Such a device can advantageously be realized inhardware as an additional access printed circuit board (PCB). The PDLSUBdevice is provided for extracting from the physical signals PS receivedfrom the physical network, e.g. from the multimedia terminal MT or fromthe data network itself, the (signaling) network protocol messages NPM.The access device PDLSUB operates bi-directionally, i.e. it can alsoreceive network protocol messages NPM and convert them back to physicalsignals to be provided to the data network and the multimedia terminalMT, respectively.

More specifically, the access device PDLSUB comprises a physical serviceaccess point PSAP for receiving from the physical network the physicalsignals PS and for decoding these signals. An adaption means PL convertsthese decoded physical signals into bit-frames and a data link protocolprocessing means DLL then extracts the additional information belongingto the data link protocol from the bit frames received from the PLdevice and thus provides the network layer protocol messages NPM througha data link service access point DLSAP to the network and transportsub-layer means NTSUB as shown in FIG. 6.

In the opposite direction, the PDLSUB means receives network protocolmessages NPM through the DLSAP from the entity connected to it, thenputs this message into a data link protocol bit frame adding the datalink protocol additional information and then the bit frame is encodedin the PL device in an electrical signal put onto the physical datanetwork through the physical service access point PSAP.

An example should illustrate the functionality of the PLDSUB part of theaccess board ALM. If the multimedia terminal MT or the data networkoperates according to a TCP/IP protocol (i.e. the data network is aTCP/IP network) then the encoding/decoding of bit frames in the PLdevice is performed according to the IEEE 802.3 standard (Ethernet)whereas the data link protocol processing device DLL forextracting/inserting the additional information belonging to the datalink protocol would be implemented in accordance with the IEEE 802.2standard (HDLC: High Definition Link compatibility).

Similarly, if the PABX controller wants to be connected to an ATM datanetwork, the PL device would be a wavelength division multiplexingdevice (PDM) and the DLL device would operate according to the ATMspecifications (ATM: Asynchronous Transmission Mode).

Therefore, whenever a different type of data network is to beintegrated, only the PL and DLL devices need to be appropriately adaptedin order to extract from the received physical signals PS the respectivenetwork protocol messages NPM. It is also possible that the PDLSUB meanscomprises a plurality of PL devices and DLL devices which arerespectively selected in accordance with the specific type of multimediaterminal and data network connected to the PABX system. Such selectioncan be performed manually or automatically by recognizing the type ofmultimedia terminal or data network connected to the PABX network.

Network and Transport Sub-layers

Another device which requires an adaption depending on the type ofmultimedia terminal or a data network specification is the networktransport sub-layer means NTSUB of the access layer means ALM. FIG. 7shows a functional block diagram of this NTSUB layer means. Thefunctionalities in FIG. 7 can be realized by a hardware printed circuitboard or corresponding functionalities realized in software. Essentiallythe network and transport sub-layers NTSUB are provided to convert thenetwork protocol messages NPM from the physical and data link sub-layerPDLSUB into the multimedia protocol messages NPM data streams in abi-directional manner.

Essentially, the network layer of the NTSUB means is constituted by anetwork protocol processing device NL which deals with the delivery ofpackets from endpoint to endpoint through the underlying network. It canalso perform control functions of the network status, congestioncontrol, etc. The network protocol processing device NL can for examplebe implemented in accordance with the Internet Protocol (IP).

The transport layer part TL of the NTSUB means adds reliability in thedelivery and fragmentation of messages. Optionally, it can also includeaccess management, security functions etc. For example, the transportprotocol processing device TL can be implemented in accordance with theTransmission Control Protocol (TCP) in its standard and secured version.

Multimedia protocol messages and data streams MPMDS received from anapplication on top of the transport layer (e.g. from the protocolhandling layer means PHLM) through a transport service access point TSAPare embedded into a Transport Protocol message TPM which is sent to thenetwork layer device NL through a network service access point NSAP. Thenetwork protocol processing means NL embeds this transport protocolmessage TPM into a network protocol message NPM which is sent throughthe data link service access point DLSAP to the physical and data linksub-layer PDLSUB as shown in FIG. 6. Since the NTSUB device isbi-directional, in the other direction network messages NPM are strippedoff the network and transport protocol additional information in theirway to their application. Thus, the output of the NTSUB means in theupward direction are multimedia protocol (signaling) messages and (data)streams extracted from the network protocol messages NPM.

For example, if the PABX wants to be connected to a data networkoperating in accordance with the TCP/IP protocol, the network layerdevice NL must be implemented in accordance with the Internet protocolIP and the transport protocol processing means TL must be implemented inaccordance with the TCP protocol. The transport service access pointsTSAP acting as kind of “sockets” or “interfaces” are implemented inaccordance with the TCP API (TCP API: Transmission Control ProtocolApplications Programmer Interface).

As another example, if the PABX controller wants to be connected to aNovell Netware data network, the network and transport layer NTSUB; NL,TL functions are both implemented in accordance with the IPX protocol.

By implementing the two devices NTSUB, PDLSUB the physical signalsreceived from the data network are processed in order to extract themultimedia protocol (signaling) messages and data streams of thecommunication received from the multimedia terminal MT and the datanetwork. As was the case in the PDLSUB means, also in the NTSUB devicethe TL and LL means can be provided several times in order to allow anautomatic or manual adaption to data networks of different protocols.

Therefore, one can say that the access layer means ALM of the inventivemultimedia controller MMC does not perform a protocol adaption as does agateway, but it provides the multimedia protocol messages and the datastreams of the communication received from the physical connection andit does so in a bi-directional way. The multimedia protocol messages anddata stream messages MPMDS are the messages which are then used in thetwo upper layers PHLM, MHL, AL as will explained below. Suchextraction/insertion of messages MPMDS is necessary in order to allowthe multimedia controller MMC to interpret signaling messages in orderto control the switching means SM (and to allow the registration,discovery and call set-up procedures).

Since the multimedia protocol and data stream messages MPMDS are usedsome detailed explanation of these messages are made hereinafter. InTelephony over Data Networks, in order to get a complete communicationbetween terminals, there are two main information sets that must bedistinguished:

-   1. Signaling. This includes the messages exchanged between peers in    order to set-up and tear down calls, invocation and execution of    supplementary services, and any other function supported by the    protocol to which these messages belong. In signaling, two main    areas can be distinguished: 1 a. Call Signaling. This includes    messages related exclusively to call-related functions, like e.g.    setting up a call, reporting that the called party is ringing etc. 1    b. Other signaling. This includes messages not directly related to    call functions. Examples of this might be registration messages,    location messages (messages used to guess where a given party is    located) etc. The signaling is characterized by its discrete nature    (one bunch of octets every n seconds, with n being a random variable    which range is, in principle, unlimited).-   2. Media. This includes the information which is the object of the    communication, i.e. the information that actually wants to be    exchanged by the users. The signaling is an accessory part of the    communication necessary for a right interworking between the    physical devices. When this information includes information    generated by intrinsically-continuous information sources like audio    and/or video sources, the transfer of this information between    parties takes the form of a more-or-less constant flow of packets    through the network, and is therefore sometimes called “stream”.

Therefore a “media stream”, “multimedia stream” or “multimedia datastream” as mentioned above refers to the information which is generatedby and exchanged between the users and which is the object of thecommunication process. Thus, the aforementioned “multimedia protocolmessages” constitute the signaling part of the multimedia protocol beingused, whilst “data stream messages” constitute the media part of saidmultimedia protocol.

Protocol Handling Layer

The protocol handling layer means PHLM resides on top of the accesslayer means ALM. The protocol handling PHLM takes care of all processesrelated to the Multimedia Protocol which is being used for themultimedia communication.

By isolating the multimedia protocol handling functions in a separatelayer the rest of the layers are made independent of the multimediaprotocol used. This means, that an H.323 protocol handling layer meanscan be replaced by a SIP protocol handling layer using the same accessand application layers. The protocol handling layer functionalities canbe again realized in hardware or software blocks.

As shown in the functional block diagram of FIG. 8, the protocolhandling layer means PHLM comprises three different devices, namely aprotocol device PCM, a control and management device CMM and a callcontrol device CCM. Through the transport service access point TSAP ofthe NTSUB sub-layer (FIG. 7) it receives the multimedia protocolmessages & data stream messages MPMDS and forms the applicationprimitives AP and the call-related application primitives CRAP therefromin a bi-directional manner. The AP primitives and CRAP primitives arerespectively provided to the application layer AL.

In a more generic way, one can understand the significance of theapplication primitives AP and the call-related application primitivesCRAP by considering the actual purpose of the protocol handling layer.The Protocol Handling layer is in charge of checking the correctness ofthe sent and received multimedia protocol messages, and of the mappingto/from Application primitives and multimedia protocol messages.Therefore it does not send or receive any information belonging to themedia part of the protocol. This information is only processed by theMedia Handling Layer (in a similar way, the Media Handling layer willnever send, receive nor process a Multimedia protocol message. It onlyhandles media streams, i.e. continuous flows of packets carryinginformation generated by the users of the communications system).

For example, if a party places a call to another party, at a givenmoment, the Protocol Control block PCM receives a Multimedia protocolmessage from its underlying Transport layer. The Protocol Control blockwill decode the message, check that the information contained in it iscorrect according to the protocol specification, and handle the messageup to the Call Control block CCM (since the Protocol control block findsout that this is a call set-up message, therefore call-related). TheCall Control CCM block will then invoke an Application primitive thatmight be called “receiveCall(E.164 number)”. The Application layer thenwill execute the procedures in it contained for handling the receptionof a new call from a remote party.

Thus, the protocol control device PCM performs an encoding/decoding ofthe multimedia protocol messages MPMDS and controls/checks thecorrectness of these messages in accordance with the multimedia protocolspecification.

On the other hand, the control and management device CMM processes allmessages from the protocol control device PCM which are not directlybelonging to the call signaling part of the multimedia protocol(messages). For example, the control and management device CMM processesthe discovery and registration messages of the discovery andregistration processes shown in FIGS. 13 a, 13 b and 13 c to beexplained below. It also processes the messages for address translation,resource management and any other service which the PABX provides to themultimedia terminal MT. Thus, the output of the control and managementdevice CMM are the application primitives AP which are control messagesoutput to AL. That is, the Application primitives generated by theControl and Management block are delivered to the Application layer ALthe same as those primitives generated by the Call Control block.

On the other hand, the call control device CCM maps call-relatedapplication primitives CRAP to call signaling messages of the multimediaprotocol and vice versa. Thus, the call-related application primitivesCRAP are a reflection of the actual call signaling messagesreceived/transmitted to/from the multimedia terminal MT and the datanetwork, respectively. The call control device CCM also checks thecorrectness of the received messages or the correctness of the invokedprimitive against the call status, according to the multimedia protocolspecification. That is, the Application primitives generated by theControl and Management block are delivered to the Application layer ALthe same as those primitives generated by the Call Control block.

As indicated in FIG. 8, the protocol control device PCM can preferablybe connected to several transport service access points TSAP, forexample in case that the call signaling messages and the non-callsignaling messages of the multi media protocol use different transportservice access points TSAP.

For example, if the multimedia protocol used by the multimedia terminalsMT and the data network, respectively, is the H.323 protocol, theprotocol control device PCM is implemented as a PER encoder/decoder, thecontrol and management device CMM is an implementation of the H.225.0RAS protocol of a H.323 gatekeeper GK and the call control block CCM isan implementation of the H.225.0/Q.931 & H.245 protocol of the H.323gatekeeper. As explained before, if the multimedia controller MMC is tooperate in accordance with a plurality of different data networkprotocols, several different control devices PCM, CMM and CCM can beprovided and can be selected (manually or automatically) depending onthe type of multimedia protocol used in the data network.

Media Handling Layer

In the context of a layer structure, the media handling layer device MHLis on top the access layer ALM and is therefore at the same level as theprotocol handling layer means PHLM. The media handling layer device MHLprocesses all messages related to the handling of connections formultimedia transmissions between multimedia terminals MT and the PABXnetwork. It is important to keep this layer as isolated as possible fromthe protocol handling layer MHL which thus allows the handling of callswhich do not use the switching resources of the PABX. As shown in FIG. 9a, the media handling layer means MHL receives through one or moretransport service access points TSAP from the network and transportlayer device NTSUB the multimedia streams MMS of the multimedia protocolmessages & data stream messages MPMDS. MHL also receives applicationprimitives AP from the application layer AL which previously receivedanother related primitive from the protocol handling layer means PHLM.

For example, the protocol message triggers the sending of a primitivefrom PHLM to the Application Layer, and then the Application Layer sendsthe actions (such as transmission of data stream for which a protocolmessage is treated by PHLM).

On the basis of these messages MMS, AP the media handling layer meansMHL directly interfaces with the PABX switching sub-system SW byoutputting messages PIMFM having the PABX's internal media format. Thus,on the basis of the control application primitives AP the actualconverted multimedia data streams MMS are provided to the switchingsub-system SW.

As shown in FIG. 9 a, the media handling layer MHL comprises a mediagateway device MGM and media control device MCM.

The media gateway device MGM converts the actual multimedia datainformation messages MMS between the format used in the multimediaprotocol being supported and the internal PABX's switching sub-systemformat. The media gateway device MGM can be implemented by means ofhardware or software. If implemented in hardware, a PCB (PCB: PrintedCircuit Board) is added to the PABX which implements all the necessaryelements for transferring/converting the multimedia information messagesMMS between the data network and the PABX's switching sub-system SW.

FIG. 9 b shows an embodiment of the media gateway device MGM whichcomprises a plurality of coders COD1, COD2 . . . CODn which arecontrolled with coder control messages CC from a coder management deviceCODM. The coder management device CODM operates on the media controlprotocol. The coder management device CODM is part of the media controldevice MCM. The Codecs COD1, COD2 . . . CODn encode/decode informationstreams. For example, the audio codec encodes/decodes an audio stream(i.e. a continuous flow of audio samples) using a given coding format.For instance, the voice in PCM links is coded according to the ITU-Tstandard G.711. In H.323, the voice might be encoded according to manydifferent standards like G.723, G.729 etc. To convert between G.711 ande.g. G.723 a codec is necessary. On the other hand, TDM switches asthose used in PABXs use the G.711 format. Therefore, to input a voicestream encoded according to e.g. G.723 to the PABX switch, a codec mustfirst convert the voice samples from the G.723 coding scheme to theG.711 coding scheme. The Codecs must be controlled by some device whichconfigure the input and output coding scheme and order the codec tostart coding/decoding. This is the function of the Codec Managementblock CODM.

Furthermore, the media control device MCM in FIG. 9 a receivesapplication primitives AP sent from the application layer as a responseto a primitive received at the application layer from the protocolhandling layer means PHLM shown in the FIG. 8. The media control deviceMCM uses these application primitives (control signals) AP for settingand tearing down connections between the transport service access pointTSAP and the PABX's switching sub-systems SW and controls the mediagateway device MGM to do whatever is appropriate by means of the mediacontrol protocol. The media control device MCM can have control of oneor more media gateway devices MGM. Basically the Media Gateway MGMconverts to/from different coding schemes as ordered by the MediaControl block MCM. The Media Control protocol MCM is the protocolunderstood by the Media Gateway MGU and the Media Control blocks MCU,and is composed of primitives like “connect codec to TSAP xxx . . . ”,“disconnect codec”, and “start converting from G.711 to G.723”.

For example, if the multimedia data network MMN uses a TCP/IP networkfor transport then the media gateway device MGM must be animplementation of the RTP/RTCP protocols (RTP: Real Time Protocol; RTCP:Real Time Control Protocol) and it must contain a transcoding devicewhich converts between the coding standards used on the RTP side (e.g.H.261+G.729) and the PCM coding (G.711) used internally in the PABXswitching sub-system SW. Summarizing, one can say that the PHLM cannotcontrol the MHL, and therefore the MHL will never receive any primitivefrom the PHL. The layer which sends primitives to the MHL in order toset up transcoding paths in this MHL is the Application layer.

Application Layer AL

This layer is in a layer context in control of the underlying layersPHLM, MHL and AL. It has direct interfaces with the control blocks inthe PABX switching means in order to get interworking between atelephony terminal TT and multimedia terminals MT and manages theinterworking between two and more multi media terminals MT. As indicatedin FIG. 4, the application layer device AL comprises a basic servicesdevice BSM and a supplementary services device SSM which arerespectively shown in FIG. 10 and FIG. 11.

The basic services device BSM comprises a call set-up means CSM forsetting up calls (media+signaling connections) between multimediaterminals MT and telephony terminals TT, no matter what their types are.A call disconnection means CDM is responsible for tearing down calls(media+signaling connections) previously set up between terminals, nomatter what their types are (MT or TT). A status control means SCMcontrols the status of calls in order to ensure that an end-to-endcommunication is held when the physical resources of the switching meansSW allow this. A resource use control means RUM manages the data networkresource utilization by multimedia terminals MT. A conversion means CMperforms a translation between the multimedia terminal's addresses(e-mail address, URL address, etc.) and the telephony terminal'saddresses (e.g. E.164 addresses).

Whilst the conversion means CM is for example not used in the flow chartin FIG. 12, indeed in FIGS. 13 a, 13 b, 13 c it is used. That is, theflowchart in FIG. 12 (which, by the way is different from the rest ofdiagrams since this one illustrates a manual process that must be doneby an Administrator or some kind of Management entity external to thesystem) actually the relationship between E:164 numbers and otheridentities like e-mail, URL, TA etc. is created. However, the CM is usedin flowcharts in FIGS. 13 a and 13 b. In FIG. 13 c, the CM itself isillustrated. It is the database on the right side of the figure. Theflowchart on the left side is used for checking that the identityprovided by the MT is correct by accessing the data in this CM. Thiswill be explained below with more details.

Finally, a call management means CMM performs the call managementthrough the use of facilities such as call information logging, trafficmanagement, call authorization/restriction, etc.

The supplementary services device SSM implements additional, value-addedfunction related to calls. The list of these functions is virtuallyendless. Additional telephony supplementary services are preferablyincluded in this device SSM. For example, the SSM device can comprise acall forwarding means CFM for call forwarding processing, a calltransfer means CTM for call transfer processing, a call waiting meansCWM for call waiting processing, a call conference means CCM forconference call set-up, a message waiting means MWM for message waitingcontrol, an operator service means OSM for operator services and a groupservices means GSM for group services (ACD: Automatic Call Distribution,Group Hunting, etc.). The supplementary services means SSM can also beextended later to new as yet not existing services related to multimedia terminals. Since the BSM and SSM are separate in two differentdevices, it is possible to add new services in the supplementaryservices device SSM without affecting the control functions of the basicservices device BSM. As shown on the right hand side in FIG. 10, thebasic services device BSM and the supplementary services device SSMperform the listed functions during communications CC between multimediaterminals MT1, MT2, between telephony terminals TT1, TT2 and betweenmultimedia terminals and telephony terminals MT2, TT1.

Operation and Maintenance Layer

This layer implements the necessary functions for setting and readingthe parameters particular to the multimedia terminals and not covered bythe PABX's generic O & M sub-system. These parameters are those whichare of use only when dealing with MTs. For instance, a Transport Addressis of no use for an analogue phone. A digital phone does not have anypassword associated to it in order to access the PABX. These and otherparameters specific for MTs are set by means of the O&M layer. As apossible list of parameters set by means of the O&M layer for MTs, thereare for example:

-   -   Transport Address    -   User Identification.    -   Password    -   URL address    -   e-mail address

However, any of these parameters might be or might not be initiated fora given MT. For example, a MT which does not require authenticationwould not have a Password associated. A MT which does not have a fixedTA (like e.g. a mobile PC) would not have a Transport Addressassociated, or perhaps it had it, but then also a Dynamic TransportAddress not initiated via O&M should exist in the system. Therefore, theOML Layer sets one or more of the aforementioned parameters depending onthe type of MT.

As shown in FIG. 11, the PABX has its own generic O & M system and theOML device implements further O & M operations for adding, removing,configuring and printing out information about access PCBs in the PABX;adding, removing, configuring and printing out information aboutmultimedia terminals which are extensions in the PABX. Furthermore, inthe OML device the functions that carry out the multimedia terminal'sspecific part of the generic call and terminal management processes inthe PABX are located. Such processes are for example the callinformation logging functions which collect data about calls such ascall duration, source and destination addresses, call cost, etc.Furthermore, it carries out traffic measurement functions which collectdata about call traffic such as the total number of calls, number offailed calls, mean and peak traffic intensity, etc. Furthermore, the OMLdevice incorporates terminal management functions such as the setting ofcategories, assigning of E.164-compliant directory numbers and printingout of terminal related information (terminal type, directory type,category) etc.

As explained above, the multimedia controller MMC in accordance with theinvention comprises a plurality of devices ALM, PALM, MHL, AL, OML whichcommunicate among each other in order to make the multimedia terminal MTa normal extension of the PABX extension space and for extracting fromthe data communication arriving in the data network protocol format therespective signaling messages which are needed for controlling theswitching resources SW and for routing the multimedia data streamsthrough the so controlled switching subsystem SW. Hereinafter, thespecial interaction of these devices is explained with reference to flowcharts in FIGS. 12–17 and a skilled person realizes on the abovedescriptions the respective usage of the devices in these procedureseven if no explicit reference is made to these blocks. Therefore, itshould be understood that an interaction of all devices is respectivelyperformed whenever one or more of the procedures described below arecarried out.

Interaction of the ISO OSI layers

In the ISO OSI reference model shown in FIG. 4, a generic architecturefor communication between peer entities is defined. By ‘peer entities’it is understood that the entities are twin, as opposed to e.g. theclient-server model where both parties have differentiated roles andfeatures.

This architecture is defined in such a way that for a given entity in agiven layer in a given party, it seems as if it was communicating with apeer entity in the same layer of the remote party. However, whatactually goes on is that said entity is communicating with anotherentity in the underlying layer in its same party. This holds true forany layer except for the physical layer which is the only one whichactually has a peer-to-peer communication with the physical layer of theremote party.

The communication between a given entity in a given layer and its peerremote entity is done by means of the aforementioned “primitives”. Eachlayer defines certain primitives used for carrying out thiscommunication. A primitive of the Data link layer might be e.g. “send adata frame to peer” if point-to-point communication, or “send a dataframe to peer at address xxx . . .” in case of a point-to-multipointcommunication.

At the application layer AL, primitives are function calls, usuallyprovided by an API (Application Programmer Interface) of the underlyinglayer. At the application layer of a telephony application, forinstance, there might be a primitive such as “startCall(E.164 number)”.

A given layer's primitives are accessible at a so-called SAP (ServiceAccess Point) as shown in FIGS. 6, 7, 8, 9 a, 9 b. The SAPs are normallypreceded by a prefix that indicates which layer the SAP belongs to.Examples of this are Transport layer SAPs (TSAPs) or Network layer SAPs(NSAPs). Therefore an entity in the Transport layer of a given peercommunicates with the Network layer of this same peer via one or moreNSAPs (it should be noted that said entity is not aware of whether it istalking to its remote peer or to its underlying layer).

Normally, one SAP is used for every instance of a communication process,in such a way that if a certain entity at let's say the Applicationlayer of one peer is holding three calls to its remote peer, then itwill “talk” with three different TSAPs of its underlying Transportlayer.

All this is to explain the communication when “A is connected to B”.Normally, this means that A and B are communicating peers at the samelayer in different machines, which establish a dialog by means of thecorresponding primitives.

As an example of this, if A is a Multimedia Terminal and B is aMultimedia Network Controller, the connection “MT is connected to MNC”means that the Application layer of the MT is talking to the Applicationlayer of the MNC, even though every primitive invoked by said MT'sApplication layer in order to send something to its peer at the MNC isactually sending a message to the MT's Transport layer, and in turn tothe MT's Network layer, and so on down to the MT's physical layer whichis the one that actually send the electrical signal to the MNC'sPhysical layer.

In view of the above explanations it should be noted that all operationscarried out in the flowcharts of FIGS. 12–17 and their associateddescriptions in the text relate to and are performed in the Applicationlayer.

The data packets and signaling packets are delivered to thecorresponding layer (Media Handling or Protocol handling, respectively)as follows. Namely, the data packets and signaling packets use differentTSAPs. The Media Handling layer accesses one TSAP, and the ProtocolHandling layer accesses a different TSAP. The MT sending a data packetwill send it to the receiving AL's TSAP used for receiving media (incase the Media Handling block was involved in the call), and will send asignaling packet to the receiving AL's TSAP used for receivingsignaling. The receiving AL's TSAP for signaling has been obtained bythe sending MT by means of the “register ack” message as will beexplained with reference to FIG. 13 b (step ST13 b 9) below. Thereceiving AL's TSAP for media might be included by the receiving AL inany call signaling message sent by the AL to the MT (e.g. the “callprogress” message).

Second Embodiment (Integration of MTs in the PABX)

It should be noted that all operations in the diagrams FIGS. 12–17 aredone by the application layer. That is whenever “Application Primitives”are referenced in the drawings or the text, this term refers toprimitives issued by/to the Application layer only, and an “ApplicationPrimitive” is never going to or coming from anywhere but the Applicationlayer.

Claim 3 of the attached claims relates to the second embodimentdescribed here and to the third embodiment described hereinafter. Alsoclaim 4 of the attached claims relates to the second embodimentdescribed here and to the third embodiment described hereinafter. FIG.12 illustrates a method according to the second embodiment of theinvention for initiating a multimedia terminal as part of the PABX'sextension space. This initiation process is necessary in order to treatthe multimedia terminal MT as a normal telephony terminal TT in thePABX's extension space.

The multimedia terminal MT when used in the data network is notidentified by a directory number (such as an E.164 number) but isidentified by data structures normally used in the data network.Therefore, the multimedia controller MMC of the PABX system must holdsomewhere the multimedia terminal's data structures comprising thenetwork and transport addresses of the multimedia terminal, securityinformation (user name, password, category profiles) of the multimediaterminal MT, the identification of the multimedia terminal in thenetwork (e.g. an e-mail address, an URL-address etc.), multimediafunctionalities (such as audio, video, data using different standardsetc.) and other related data. For example, the data structure may alsocomprise a dynamic network address of the multimedia terminal whichmight change over the time and which is thus dynamically updatedwhenever it changes.

By means of the procedure in FIG. 12 an extension is added in the O & Mdevice OML for allowing an administrator or a device to relate adirectory number in the PABX's number space to these new data structuresby means of whatever O & M operations exist.

The administrator is an entity external to the system (may be human orautomatic device) which has rights to interact with the systems's O&Mlayer. Note that square blocks in FIG. 12 represent O&M operations,which are actually carried out by the O&M layer but ordered by theadministrator. Therefore the decisions in said figure are taken by theadministrator, not by the O&M layer. For example, if the administratortries to initiate a new Directory number in the system and, whencarrying it out, the O&M layer sees that for some reason this is notpossible, the O&M layer just reports this condition to theadministrator. Then it is an administrator's task to stop the wholeprocess.

FIG. 12 shows how the relationship between the directory number and thedata structures is set up such that all existing O & M processes whichthe PABX makes available for other extensions TT are potentiallyavailable also for multimedia terminals MT.

In step ST121 the OML device creates a new directory number for themultimedia terminal MT to be added. If in step ST122 no such directorynumber is created, the process is stopped. In step ST123 a datastructure relating to the particular multimedia terminal MT to be addedis set up in a database DB which can for example be part of the OMLdevice. In step ST123 the data structure is set up with the transportaddress, identification, authentication and the capabilities of the newmultimedia terminal MT as shown in FIG. 12. Such an initiation of thedata structure can be performed by executing an inquiry/responseprocedure with the newly connected multimedia terminal MT. If in stepST124 it is determined that the data structure is confirmed to becorrect, then the administrator (manual or automatic) creates a link (arelationship) between the newly created directory number and the MT datastructure in step ST125 (which is most significant and innovative aspectof this procedure). If in step ST124 the data structure is determined tobe incorrect then the process is stopped. However, if the data structurehas been correctly set up and the link is created in step ST125, thenthe multimedia controller MMC can handle the newly added multimediaterminal MT with its specification defined in the data structure simplyas a normal PABX extension just like any other telephony terminal TT.Such a relationship is stored in the database DB for each and everynewly added multimedia terminal MT.

As mentioned before, some basic items must be set in the data structure,for example the transport address, the identification, theauthentication and the capabilities, when the multimedia terminal MT isadded. However, there may also be time-varying information such as adynamic network address of the multimedia terminal MT which can changeover time. Then, whenever this dynamic network address changes arespective updating of this entry in the data structure of themultimedia terminal MT is performed.

Therefore, one can say that the procedure in FIG. 12, i.e. setting ofthe data structures and the cross-link to a newly created directorynumber for each and every multimedia terminal MT, makes the multimediaterminal MT “visible” in. the PABX network just like any other telephonyterminal TT which is handled and processed by means of its directorynumber. That is, the administrator creates the link between directorynumber and MT's Data Structure by ordering a “link” operation to the OMLproviding the directory number and a pointer to the MT's Data Structure.

Third Embodiment (MT Discovery and Registration)

For multimedia terminals MTs which have dynamic characteristics, i.e.characteristics that may vary along time and for those which want totake advantage of freeseating, i.e. to take advantage of the possibilityof connecting to the PABX network from different access points keepingthe same user profile (i.e. using the PABX freeseating feature also forMT terminals), a discovery and registration process is necessary inorder for the multimedia terminal MT to access PABX facilities. Thus,according to the invention the MTs enjoy e.g. the PABX's freeseatingfunctions. It should be noted that there are different types offreeseating. The freeseating which is conventionally a PABX feature,means that a PABX's user is able to log-in to the PABX from any terminalno matter where or what kind of_terminal it is. By making the multimediaterminals MTs “visible” (in accordance with the invention) for the PABXas any other kind of terminal, this freeseating function, alreadyexisting in the PABX, is enabled for MTs also.

The registration process must be started by the multimedia terminal MTand must be acknowledged by the PABX multimedia controller MMC. Such aregistration process is typical if the multimedia terminal MT performs aregistration in the data network. Also in a data network the multimediaterminal MT must know the transport address e.g. of a gatekeeper throughwhich the respective protocol handling layer receives registrationmessages. Likewise, when the multimedia terminal MT whose data structurehas been set up in the database and has been linked to a directorynumber wants to access the PABX network, it must receive informationabout the transport address in which the protocol handling layer meansPHLM shown in FIG. 8 receives signaling messages and registrationmessages. This transport address of the protocol handling layer devicePHLM is then used by the multimedia terminal MT to send a registrationmessage to the PABX controller. One possibility is that manually thetransport address set in the protocol handling layer device PHLM isprogrammed (stored) in the multimedia terminal MT.

The third embodiment of the invention for discovery and registrationrelates to claim 2 and claim 10 of the attached claims and the subjectmatter of claim 3, claim 4 and claim 7 relates to both the second andthird embodiment. FIG. 13 a shows a flow chart of how an automatictransport address discovery process can be carried out. The purpose ofFIG. 13 a is to send a discovery message to a fixed known transportaddress through which one or more PABX's protocol handling layer devicesPHLM are receiving discovery messages. Every PABX controller of aplurality of PABX networks which is ready to accept the multimediaterminal in its extension domain will send back to the multimediaterminal MT the transport address through which the respective protocolhandling layer device PHLM is receiving registration admission andstatus (RAS) messages. Knowing this transport address the multimediaterminal MT can then perform a registration process as shown in FIG. 13b. the purpose of the procedure in FIG. 13 b is to allow the multimediaterminal MT to send the registration message to the obtained transportaddress of the protocol handling layer. The application layer connectedto the protocol handling layer in this address will process this messageand will send back an acknowledgement to the multimedia terminalnotifying an acceptance or rejection of the multimedia terminal MT inthe extension space of the PABX. Even if a manual setting of thetransport address is performed in the multimedia terminal, it is stillpossible to send a discovery message to the thus configured transportaddress. This could be useful for making both ways of finding out atransport address for registration in a more homogenous way. The mostimportant aspect in FIG. 13 a is the innovative aspect of the procedureto process the discovery request shown on the right hand side in FIG. 13a.

It should be noted that a prerequisite for carrying out the proceduresof discovery and registration in FIGS. 13 a, 13 b, is that the datastructures of the multimedia terminal MT have already been set inaccordance with FIG. 12.

In step ST13 a 1, ST13 a 1′ the multimedia terminal MT sends a discoverymessage including its identity to (a fixed transport address of theprotocol handling layer of) the PABX multimedia controller MMC (via theprotocol handling layer PHLM to the application layer AL of thecontroller MMC) just as if it was doing so for discovering a transportaddress in a discovery process carried out in a data network. Therefore,in FIG. 13 a the new aspects of the third embodiment of the inventionare on the right-hand side, in the algorithms of the PABX controller andnot on the left on the multimedia protocol signaling side which are wellestablished procedures in a multimedia data network.

In step ST13 a 2 the multimedia controller MMC performs an identitycheck against the identity information stored in the data structures ofthe database DB. This is done in order to find the directory number thatcorresponds to the identity information provided in the discoverymessage in step ST13 a 1.

Preferably, a discovery message in step ST13 a 1, ST13 a 1′ can containseveral identifications provided by the multimedia terminal MT (e.g. ane-mail address, a URL etc.) and therefore all of the provided identitiesare compared with the data structure(s) stored in the database DB. Ifall identities provided in the discovery message match the entries inthe set-up data structure (in the O & M layer means OML) then in stepST13 a 3 it is determined that the relationship between the createddirectory number and the multimedia terminal identification is valid.

If, however, in step ST13 a 3 one or more of the identity matchingsfail, the discovery attempt will be rejected in step ST13 a 7.

It should be noted that the identity information sent by the multimediaterminal MT could be anything allowed within the discovery message inuse. Therefore, as explained above, it is preferable to have a databaseDB in the multimedia controller MMC which relates directory numbers toany kind of identity (e-mail address, URLs etc.). As explained above,the same database DB holding the data structure can also be used forholding the user identities and the password lists associated to thenewly created directory number.

In step ST13 a 4 it is determined by the multimedia controller MMCwhether or not to admit the multimedia terminal MT in its extensionspace and if so determined in step ST13 a 5 a confirmation is determinedin step ST13 a 6. Then, the protocol handling layer means PHLM sendsback in step ST13 a 8 a message with the desired transport addressthrough which the protocol handling layer is receiving registrationadmission and status (RAS) messages. Knowing this transport address themultimedia terminal MT can now perform a registration process as shownin FIG. 13 b. The most important aspect in FIG. 13 b is the innovativeaspect of the procedure to process the registration request shown on theright hand side in FIG. 13 b.

If in step ST13 a 3 or ST13 a 5 the identity check and/or the admissionis negative a discover rejection message is determined in step ST13 a 7and is sent to MT in steps ST13 a 8′, ST13 a 8.

It should be noted that the multimedia controller MMC can also take adecision about the Transport Address which it sends back to themultimedia terminal MT which started the discovery process. If themultimedia controller MMC has knowledge of different PSAPs and theircorresponding Transport Addresses, it could decide to send any of theseTransport Addresses to the multimedia terminal MT in the discoveryacknowledge message. In this way, the multimedia controller MMC is ableto direct the multimedia terminal MT to register using another PSAPwithin the multimedia controller MMC scope, or even a PSAP within thescope of a different multimedia controller MMC in case the multimediacontroller MMC receiving the discovery message had knowledge ofTransport Addresses associated to said PSAP.

The criteria used by the multimedia controller MMC to decide whichTransport Address is to be send back to the multimedia terminal MTsending the discovery message comprise one or more of the followingcriteria:

-   -   a Transport Address associated to a PSAP under low load        conditions;    -   a Transport Address associated to a PSAP which is working        properly;    -   a Transport Address associated to an external (under the scope        of another multimedia controller MMC) PSAP which is less loaded        than this MMC's PSAPs;    -   a Transport Address associated to an external (under the scope        of another multimedia controller MMC) PSAP which corresponding        MMC is supporting a lower signaling load than the deciding        multimedia controller MMC.

In step ST13 b 1, ST13 b 1′ the multimedia terminal MT sends aregistration message to the transport address of the protocol handlinglayer means PHLM which has been either manually set or obtained via thediscovery procedure of FIG. 13 a.

In step ST13 b 1′ the message is passed on to the application layermeans AL. In step ST13 b 2 the multimedia controller MMC performs anidentity check of the identity, user name and password and optionally ofadditional dynamic data. This check procedure is carried out inaccordance with FIG. 13 c. The identity check procedure in FIG. 13 c isone of the important aspects of the present invention.

If the provided information is determined to be valid in step ST13 b 3,in step ST13 b 4 the data structure(s) of the multimedia terminal MT islocated in the database DB. This is done by using the information whichhas been checked in step ST13 b 2 and which was provided in theregistration message ST13 b 1. If a match to one of the data structuresis found in step ST13 b 5 (“YES”) if a security check in step ST13 b 2′where security information contained in the registration message ischecked against security information in the data structure (data base)is completed positively in step ST13 b 2′′, then a possible updating ofthe entries in the data structure of the multimedia terminal MT isperformed in step ST13 b 6. If the result is confirmed in step ST13 b 8then a registration acknowledgment message comprising a transportaddress through which the protocol handling layer is receiving callsignalling messages is sent back to the multimedia terminal MT in stepST13 b 9, ST13 b 9′. If the result is no in step ST13 b 3 or ST13 b 5then a rejection message is sent to the multimedia terminal in step ST13b 7 and sent in step ST13 b 9′, ST13 b 9′, ST13 b 9 to the multimediaterminal via the application layer ALM and the protocol handling layerPHLM.

FIG. 13 c shows the step ST13 b 2 of FIG. 13 b with more details. Thatis, FIG. 13 c shows the algorithm which allows the multimedia controllerMMC to verify a given MT's identity.

As shown in FIG. 13 c the database DB containing the data structures ofthe multimedia terminals MT also has three different registers IM-INDX,URL-INDX, E.164-INDX holding the respective e-mail addresses, URLidentities and E.164 identities which are allowed to be processed in thePABX network. In steps ST13 c 1, ST13 c 4, ST13 c 7 it is respectivelychecked whether the registration message sent from the multimediaterminal MT contains an e-mail address, a URL or a E.164 directorynumber. In step ST13 c 2, ST13 c 3; ST13 c 5, ST13 c 6; ST13 c 8, ST13 c9 each of the identities contained in the registration message arechecked against the entries in the EM-INDX, URL-INDX and E.164-INDXregisters. If the entries are respectively found (yes in step ST13 c 3,ST13 c 6, ST13 c 9) then step ST13 b 3 in FIG. 13 b continues with stepST13 b 4, i.e. it tries to locate the data structure and the directorynumber corresponding to the multimedia terminal MT whose identities havebeen positively checked in FIG. 13 c.

Although in FIG. 6 only one physical signal access port PSAP is shown,preferably the PABX network may have several PSAP access points. Ifdifferent multimedia terminals MT carry out the procedure in FIG. 13 aand/or FIG. 13 b the multimedia controller MMC can provide to each ofthe registering multimedia terminal MT a different transport addressduring the registration process. The multimedia controller MMC can thusdistribute the signaling load to different physical signal access pointsPSAPs. The optimal assignment of transport addresses to differentmultimedia terminals MT can be carried out in different ways dependingon the procedure which is used in the multimedia terminal for obtainingthe transport address for registration. In a fist case “manual” thePABX's application layer means AL receives the registration requestthrough the PSAP, does a series of checks to decide which PSAP is moresuitable for being used by the multimedia terminal and once this isdecided the multimedia controller MMC delivers the transport address ina registration acknowledge message in step ST13 b 9. Thus, the deliveredtransport address belongs to a transport address range of a particularPSAP. In an automatic procedure (or a manual procedure with a previousdiscovery) the PSAP checking is done during the discovery process.

The multimedia controller MMC can determine which transport address tosupply to the registering (or discovering) multimedia terminal MT basedon the following considerations: the less loaded PSAP, the PSAP with thelowest mean load, the PSAP whose physical elements are working or thePSAP to which the smaller number of MTs have been assigned.

Therefore, during the discovery and registration processes themultimedia controller MMC can advantageously distribute signaling a loadfrom various multimedia terminals MT to different PSAPs by providingdifferent transport addresses based on the signaling load distribution.

The usage of the transport addresses is therefore as follows. Asexplained above, the transport addresses TA The TAs are the addressesused at the Transport layer. However, a given Transport layer messagewhich is to be sent to a given Transport entity addressed by its TA,must sooner or later go through two PSAPs (one on the message sender andanother one on the message receiver). The source PSAP (the one used onthe message sender) is not relevant for finding the message receiver,but the destination PSAP (the one used on the message receiver) must, inone or other way, be obtained at some layer in the message sender beforeputting the message onto the physical medium.

In order to be able to send a Transport layer message to a Transportentity in the network, a PSAP which may access said entity must belocated. Consequently some association between PSAPs and TAs must existsomewhere in the network and must be accessible for Transport entitieswilling to send a given message to a given TA. Therefore, on the basisof a given TA a corresponding PSAP can be identified. An Applicationlayer then then knows what TAs correspond to the PSAPs it is controlling(which are those in the same machine as said Application layer runs) anddelivers to another Application layer of the receiver a TA thatcorresponds to one of these PSAPs selected according to certainconditions (e.g. in accordance with the distribution of the signalingload.

Fourth Embodiment (Basic Call Set-up Procedures)

As explained above, the multimedia controller MMC according to the firstembodiment having the devices explained in FIGS. 5–11 is capable todirectly treat the multimedia terminal MT as an extension of the PABXnetwork in accordance with the second embodiment and in accordance withthe discovery and registration procedures in accordance with the thirdembodiment. Thus, the multimedia terminal MT can be made “visible” inthe PABX network and thus signaling messages sent by a recognized andregistered multimedia terminal MT can be sent to the multimediacontroller MMC and can be used therein for controlling the switchingsubsystem SW of the PABX network based on the contents of the soreceived recognized and interpreted signaling messages.

Hereinafter, with reference to the flow charts in FIGS. 14, 15 a, 15 b,15 c, 15 d basic call set-up procedures where such a control ofswitching resources is performed on the basis of signaling messages willbe explained in accordance with the fourth embodiment with theinvention. The fourth embodiment of the invention relates to claim 1andclaim 11, 12, 13 of the attached claims. All steps in FIG. 14 relate tothe new innovative concept of the invention.

For these call set-up procedures the following devices (layers) of themultimedia controller MMC shown in FIG. 4 are generally necessary. For acall set-up the multimedia terminal MT exchanges call signaling messageswith the multimedia controller MMC. These call signaling messages arepart of the multimedia protocol messages MPMDS provided to the protocolcontrol device PCM of the protocol handling layer device PHLM shown inFIG. 8 from the transport service access points TSAP of the network andtransport sub-layer device NTSUB shown in FIG. 7. The call controldevice CCM in FIG. 8 which is also part of the protocol handling layerdevice PHLM will provide a mapping between these signaling messagesMPMDS and the call-related application primitives CRAP provided to andunderstood by the application layer device AL.

This “mapping” comprises the task carried out by the Protocol Controlblock, which on reception of a given Multimedia Protocol message,generates the corresponding Application Primitive which is then sent tothe Application layer. In the same way, this mapping covers the casewhere the Application layer generates an Application primitive which itsends to the PHL. Said primitive is then mapped to a correspondingMultimedia Protocol message. This scheme allows the Application layer tobe independent of the Multimedia Protocol used, since if said protocolchanges, only the PHL is affected (as long as the Application Primitivesremain unchanged).

Considering the configuration in FIG. 2 or in FIG. 3, whenever a call isset-up between two or more multimedia terminals MT, two or moretelephony terminals TT or between one or more telephony terminals TT andone or more multimedia terminals MT there are cases where the internalPABX switching sub-system resources SW are necessary for transferringthe media data streams and cases where it is not necessary. The rulesthat govern the seizure of internal PABX switching resources SW fortransferring the media streams between the terminals involved in a callare the following.

Firstly, in the conventional case, when one or more terminals involvedin the call are not multimedia terminals MT, then the switchingresources SW of the circuit switched network PABX for that call must beseized. This is the case where for example two telephony terminals TTconventionally use the PABX system.

Secondly, if all terminals involved in the call are multimedia terminalsMT and it is not possible to directly set-up an end-to-end network pathbetween them, then the switching resources SW must also be seized forthat type of call.

Thirdly, if the terminals involved in the call are multimedia terminalsMT and there is the possibility to set-up an end-to-end IP network pathbetween them, but the multimedia terminals MT do not support a commoncoding scheme for the media streams to be exchanged, then also switchingresources SW of PABX system must be seized for setting-up the call. Thatis, in such a case the conventional call set-up routing through theswitching resources SW of the PABX system is necessary. With commoncoding scheme is meant that the coding of digital data for each of themedia streams sent from the two different multimedia terminals MT isdifferent. With a “common coding scheme” is meant a coding standard(i.e. G.711, G.723, H.261 etc.) which can be encoded/decoded by bothparties. If one MT party encodes voice according to G.711 and the otherMT party can only decode voice according to G.723, then voicecommunication between these parties would be impossible without a commoncoding scheme.

Fourthly, if all the terminals involved in the call are multimediaterminals MT, it is possible to set-up an end-to-end network pathbetween them, all of them support at least one common coding standardfor the media schemes to be exchanges but the service level delivered bythe data network is not sufficient enough for the purpose ofcommunication, then optionally switching resources SW may be seized forthat call.

In the aforementioned first to fourth cases the call is either routedonly through the switching means of the PABX system (first to thirdcase) or the switching resources SW are used as supplement to therouting possibilities already provided by the data network. If theswitching resources SW of the PABX system are to be used for setting upthe call for routing the multimedia data streams between the terminals,of course no modification in the actual PABX switching resources SWshould be performed since otherwise the switching resources SW wouldalso have to be adapted to the specific type of data network.

In order to not impose modifications in the already existing PABX'ssoftware, the multimedia controller MMC of the present inventiondecides, on the basis of the signaling information received from themultimedia terminals, whether switching resources SW must exclusively oradditionally be used for the set-up of a call. In particular, it is theapplication layer device AL connected to the multimedia terminals MTwhich can decide whether such resources are necessary. If the multimediacontroller MMC performs the decisions as to whether or not theseswitching resources are necessary, the PABX's core software remainunaffected and the decision process is generic for all kinds ofextensions (multimedia terminals MT and telephony terminals TT).

The basic requirement that the application layer device AL of themultimedia controller MMC performs such decision is that thisapplication layer device AL which is connected to one multimediaterminal MT knows the type of extension to which its peer entity isconnected. The term “connected” in this case means that the Applicationlayer in the MT exchanges messages with the Application layer in the MMCvia their respective Access layers. So in this case “connection” meanspeer-to-peer connection, although the messages exchanged actually gothrough several layers down and up in order to travel from peer to peer.The term “extension” here refers to a TT. The term “peer entity” heremeans that the AL handling one call between one MT and another terminalmust know that said terminal is a TT. In other words, the applicationlayer AL must know the type of terminals (MT or TT) that are involved inthe call, because if the call is between a MT and a TT, then use ofPABX's switching resources SW is necessary (since MTs and TTs usedifferent transport networks, and the only interconnection between saidnetworks is the PABX's switch).

Once, the application layer means AL knows the type of extension towhich is peer entity is connected, the process shown in FIG. 14 iscarried out. FIG. 14 basically is a flow chart which shows how themultimedia controller MMC decides whether internal switching resourcesSW should be used for the communication. The switching resources seizurealgorithm in FIG. 14 is used in the application layer means ALA justafter step ST15 a 5 in FIG. 15 a and after step ST15 d 1 in theapplication layer means ALA in FIG. 15 d.

Step ST141 is entered once the multimedia controller MMC recognized acall set-up message from any connected (or registered) extension(multimedia terminal MT or telephony terminal TT). Having performed thediscovery and registration procedures of FIGS. 12, 13, the multimediacontroller MMC can recognize whether the extension which sends a callset-up message is a multimedia terminal MT or not. This is so becausethe multimedia terminal MT, when sending the call set-up message, willsend this call set-up message to the transport address with which it hasbeen provided during the registration and it will also include anidentification and authentication and information about itscapabilities. Thus, by matching these information to the data structureset-up for the (registered) multimedia terminals MT in the data base DB,the application layer means AL can recognize whether the call set-upmessage comes from a multimedia terminals MT or a telephony terminal TT.If the answer in step ST141 is “no”, then the call is to be set up to atelephony terminal TT which automatically requires the use of switchingresources SW of the PABX in step ST148. That is, the flow diagram inFIG. 14 is executed by the application layer means ALM that receives acall setup message from an MT. This call setup message contains thecalled party's E.164 number (or another identification in case of calledparty is a MT). From this_called party identification the AL canidentify whether the called terminal is MT or TT.

However, if a multimedia terminal extension is recognized in step ST141,then step ST141 checks, whether an end-to-end network path can beset-up. With end-to-end network path is meant a direct path or routewithin the data network and not within the PABX. To check whether such anetwork path is possible in step ST143, an intermediate connectivitytest can be performed. Preferably, the multimedia controller MMC cansend some test packet to the called multimedia terminal MT. The calledmultimedia terminal MT is to send back the test packet unmodified whichindicates that the network path is possible. If the data network is anIP network, a so-called “ping packet” can be used as a test packet totest whether an end-to-end network path is possible. If the end-to-endnetwork path is not possible in step ST143, then it is of coursenecessary to seize switching resources SW in step ST148. It should benoted that the multimedia controller MMC in this case is onlyresponsible for initiation of the sending of this test packet to theconnected multimedia terminal MT on the basis of the signaling messagesfrom a calling multimedia terminal. The PABX switching resources areactually not used during the sending of this test packet.

Even if the network path through the data network has been confirmed instep ST143, in step ST144 the capabilities of the connected multimediaterminal MT must be checked. With capabilities is meant here for examplewhether the multimedia terminal supports audio, video, and/or otherdigital coding schemes. In order to check these coding schemes, theapplication layer device AL of the multimedia controller MMC sends tothe remote application layer device AL of the called multimedia terminala coding standard request to inquire about the coding standards whichare supported in the multimedia terminal MT. When the called multimediaterminal MT responds with a message containing the supported codingstandards, these received coding standards are compared with the codingstandards supported by the calling multimedia terminal MT in theapplication layer AL in order to find out, whether there are any codingstandards in common between the calling and called multimedia terminalsMT. As may be noted, the application layer AL can directly send such arequest message as a signaling message to the called multimedia terminalMT by using the respective messages described with reference to FIGS. 5,6, 7, 8, 9 a, 9 b. If in step ST145 it is determined that there are nocommon coding standards, then switching resources SW of the PABX must beused, i.e. the multimedia streams MMS must be converted by the mediagateway device MGM to be routed as converted data streams PIMFM havingthe PABX's internal media format through the switching sub-system SW ofthe PABX. The aforementioned procedure is for detecting the codingschemes supported by the called terminal and is one possible way toobtain this information. However, the preferred procedure is that the ALtalking to the calling terminal (the one that sends the call setupmessage) uses the called terminal's identification provided in saidmessage to access the database and find the called terminal's datastructures. These structures hold, between other data, the terminal'scapabilities, i.e. the coding schemes of the called terminal. The firstmentioned method might be used in case said data structures do not holdthe terminal's capabilities at all.

Regarding the implementation in FIGS. 5–9, in these figures PIMFM referto data; and AP, CRAP refer to signaling (they are ApplicationPrimitives). MPMDS refer to both data and signaling. Note that theAccess layer is a common resource which does not distinguish betweendata and signaling. The Access layer just receives something from thephysical network and sends it up to the upper layers in form of apacket.

As explained above, the data packets and signaling packets are deliveredto the corresponding layer (Media Handling or Protocol handling,respectively) as follows. Namely, the data packets and signaling packetsuse different TSAPs. The Media Handling layer accesses one TSAP, and theProtocol Handling layer accesses a different TSAP. The MT sending a datapacket will send it to the receiving AL's TSAP used for receiving media(in case the Media Handling block was involved in the call), and willsend a signaling packet to the receiving AL's TSAP used for receivingsignaling. The receiving AL's TSAP for signaling has been obtained bythe sending MT by means of the “register ack” message as explained withreference to FIG. 13 b (step ST13 b 9). The receiving AL's TSAP formedia might be included by the receiving AL in any call signalingmessage sent by the AL to the MT (e.g. the “call progress” message).

If in step ST145 it is determined, that in addition to the possibilityof setting-up a direct end-to-end network path through the data networkand also the coding standards of the calling and called multimediaterminals MT are the same, it may still be the case that the datanetwork service level is insufficient for performing a good dataexchange through the data network. Therefore, in step ST146 the datanetwork service level is sensed. The following procedure can be used inorder to test the data network service level. For this purpose, theapplication layer AL again sends a test packet with a time-stamp to thecalled multimedia terminal MT. The called multimedia terminal MT shouldtime-stamp the packet also when it is sending it back. When receivingback the sent-out test packet, the application layer device AL candetermine the round-trip delay time existing in the path between thecalling and the called multimedia terminal MT. If the data network is anIP-network, a so-called “ping packet” can be used.

Another possibility is that the multimedia controller MC instructs somedevice in the data network to compute statistics about the data networkstatus. The application layer device AL of the multimedia controller MMCcan then sent an inquiry message or wait for a response message from thestatistics computing device to obtain information about delay, packetloss etc. Thus, the multimedia controller MMC shown in FIG. 4 canactively communicate with the multimedia terminal MT or a further unitin the data network by exchanging signaling messages in order todetermine not only the possibility of a direct network path and thematching of the coding schemes but also the data network service level.If in step ST147 it is determined that the service level is acceptable,then only in this case the multimedia controller MMC has decided on thebasis of exchanging the signaling messages with the called and callingmultimedia terminal MTq that no switching resources SW of the PABX arenecessary.

If however the answer in step ST141, ST143, ST145 and ST147 is negative(“no”) then invariably there is the necessity of at least additionallyusing switching resources SW of the PABX switching sub-system in stepST148. In order to seize switching resources in the PABX's internalswitch (i.e. in the switching sub-system SW of the PABX), two differentprocedures can be used in step ST148. Either the local multimediacontroller application layer AL requests the resources from the PABX orthe local multimedia controller application layer AL leads its connectedpeer entity to seize the resources from the PABX.

With “connected peer entity” is meant the AL talking to the other MT.For example, in FIG. 15 a there are two ALs involved in the call. Thisis the case when the PABX has a distributed architecture (as is assumedin FIG. 15 a). In this architecture the calling and called MT might becontrolled by different modules of the PABX. Few PABXs in the markethave however this distributed architecture. FIG. 15 c shows the casewhere AL A and AL B are merged into one ALA, skipping all signalsbetween them ALA and ALB. However, the function is the same as in FIG.15 a. FIG. 15 c is the so-called non-distributed architecture orcentralized architecture and FIG. 15 d shows the corresponding flowcharts (all the steps in FIG. 15 d relate to the innovative aspects ofthe present invention). In FIG. 15 c the most important aspects of theinvention are the performing of the source and destination transportaddress selection algorithms.

If no PABX switch congestion can take place, then both procedures aresuitable in ST148. But if the PABX switch congestion may take place, thesecond alternative is preferable. The reason is that when a switchcongestion occurs in the PABX, in the first alternative the call set-upis lost since the calling party cannot proceed with the call set-upbecause a switch path is needed.

However, if in the second alternative the remote peer entity finds aswitch congestion, it can report this congestion back to the callingapplication layer AL (in the calling multimedia terminal MT) which canthen go on with the call by e.g. requesting some supplementary serviceon that call (call-back for instance).

During the call set-up phase one multimedia terminal MT and the PABXmultimedia controller MMC must exchange transport addresses to whichthey are supposed to send their media streams. The question as to whichtransport addresses are used is also influenced by the result of theswitching resources seizure algorithm described above.

As explained above, the application layer of the multimedia controllerconnected to the called multimedia terminal MT must send a transportaddress about the PABX's physical service access point PSAP (FIG. 6)selected for receiving not only the signaling but also the media datastreams of the call. If the application layer forwards a transportaddress of a PSAP, it is clear that switching resources have been seizedfor the call. Alternatively, the application layer connected to thecalling MT forwards the transport address of the remote MT which is acase in which all remote terminals involved in the call are multimediaterminals MT and it is thus not necessary to seize switching resourcesSW. The algorithm in FIG. 14 applies to calls MT->MT and MT->TT. Incalls TT->MT, it is the PABX core SW which will have seized switchingresources for the call, as it does for a normal TT->TT call. Thereforeit is not necessary that the AL talking to the called MT seizesswitching resources for the call.

FIG. 15 a shows a signaling diagram of a call set-up between twomultimedia terminals MTA, MTB in a PABX with a distributed architecture.The most important aspects of the present invention in FIG. 15 a is theinternal signaling between ALA and ALB. The moments when a decisionabout a transport address for media streams that is sent to each MT istaken are marked with black dots. FIG. 15 b (where all steps are part ofthe innovative concept of the invention) shows a flow-chart which iscarried out at the black points in FIG. 15 a. FIG. 15 b in particularshows the signaling that internally takes place in the PABX controllerwhen setting-up a new call using a distributed architecture PABX. Inparticular, the algorithm in FIG. 15 b is used in the application layermeans ALA just after step ST15 a 11 in FIG. 15 a and in the applicationlayer means ALB just after step_ST15 a 6 in FIG. 15 a.

In step ST15 a 1 the multimedia terminal MTA sends a call set-up messageincluding its own transport address to the application layer ALAconnected to the multimedia terminal MTA. In steps ST15 a 2, ST15 a 3,ST15 a 4 the application layer ALA forwards the transport address of thefirst multimedia terminal MTA to the application layer ALB connected tothe called multimedia terminal MTB. In steps ST15 a 5, ST15 a 6switching resources of the PABX core switching resources SW are seized.The switching resources seizure algorithm in FIG. 14 is used in theapplication layer means ALA just after step ST15 a 5 in FIG. 15 a. Thealgorithm in FIG. 15 b is used in the application layer means ALA justafter step ST15 a 6 in FIG. 15 a.

As shown in FIG. 15 b, after the switching resources are seized in stepST15 a 5, ST15 a 6, the application layer ALB performs steps ST15 b 1 orST15 b 2. If the switching resources are seized, i.e. switchingresources SW of the PABX are used, the transport address is determinedto be the own seized transport address from the protocol handling layerof the multimedia controller MMC. If no resources are seized, then ofcourse the transport address is determined to be the transport addressof the called multimedia terminal. That is, when selecting a transportaddress corresponding to one of the PABX's (i.e. when internal switchingresources for one call have been ceased in steps ST15 a 5, ST15 a 6) instep ST15 b 1, it is possible for the application layer AL connected tothe MTA to select the transport address that falls within certain PSAP'stransport address ranges according to a series of rules. This is mostuseful when the PSAP are grouped by PCBs, i.e. there are several PCBs inthe PABX with one PSAP each. Therefore, the application layer can decideon the basis of the following rules through which PSAP (PCB) themultimedia data streams are to be routed when switching resources areseized.

If several PSAPs are used then the provision of the transport address instep ST15 b 1 can be based on the less loaded PSAP, the PSAP with thelowest mean load, the PSAP whose physical elements are operational orthe PSAP, which has more free connections to the PABX's internal switch.In this way, if one of the PSAPs is overloaded or does not haveavailable connections to the internal PABX's switch (a switchconnection) the media data streams can be routed to a different PSAPwithin the PABX, such that a communication is still possible. Therefore,by providing a special transport address of one of its PSAPs themultimedia controller MMC can route the data streams through differentPSAPs when switching resources are seized in order to distributecall-related media information. Therefore, on the basis of the signalinginformation the multimedia controller MMC does not only determinewhether or not switching resources must be used but it can alsodetermine how to distribute the various multimedia data streams throughdifferent PSAPs if the switching resources are determined to have to beused.

If in step ST15 b 3 it is determined that there is already a connectionto the calling party (A-party) then a call progress is sent and if it isnot connected to the A-party, a call set-up is sent in messages ST15 b4, ST15 b 5. This is also indicated with steps ST15 a 7 and ST7 a 8 inFIG. 15 a 8 in FIG. 15 a. In steps ST15 a 9, ST15 a 10, ST15 a 11 themultimedia terminal MTB responds with its transport address and likewiseat the black point the transport address determination in FIG. 15 b isrepeated (the algorithm in FIG. 15 b is used in the application layermeans ALA just after step ST15 a 11 in FIG. 15 a.) That is, also in thereverse direction for the transmission of data from the multimediaterminal MTB to the multimedia terminal MTA a transport address for thepossible usage of switching resources of the PABX is determined.Finally, in step ST15 a 12 the transport address is provided to themultimedia terminal MTA in a called progress message.

FIG. 15 d shows a flow chart similar to FIG. 15 b for a none-distributedarchitecture PABX relating to the call setup shown in FIG. 15 c. In stepST15 c 1 a call setup message is sent from the multimedia terminal MTAto the application layer ALA wherein the call setup message contains, asin step ST15 a 1 in FIG. 15 a, the transport address of a multimediaterminal MTA. Then a source transport address selection is carried outas shown in FIG. 15 d. First, in step ST15 d 1 switching resources areseized. The switching resources seizure algorithm in FIG. 14 is used inthe application layer means ALA just after step ST15 d 1 in theapplication layer means ALA in FIG. 15 d. When in step ST15 d 2 it hasbeen determined that the switching resources have been seized, then thesource transport address is to be determined the own seized transportaddress in step ST15 d 3. If there are no switching resources seized instep ST15 d 2, then the source transport address is determined to be thetransport address of the multimedia terminal MTA as contained in thecall setup message in step ST15 c 1. In step ST15 d 5 the call setupmessage is sent. Then the procedure carries on with step ST15 c 2 wherethe call setup message including the determined source transport addressis directed to the multimedia terminal MTB. A call progress message isreturned in step St15 c 3. It contains the transport address of themultimedia terminal MTB (i.e. the called multimedia terminal MTB).Subsequently the destination transport address selection is carried outas shown in FIG. 15 d.

Similarly, as in step ST15 d 1, in step ST15 d 6 it is determinedwhether there are any switching resources in use. If there are anyswitching resources in use, then in step ST15 d 7 the destinationtransport address is determined to be the own seized transport address.If there are no switching resources in use in step ST15 d 6, then thedestination transport address is determined to be the transport addressof the calling multimedia terminal MTA. A call progress message is sentin step ST15 d 9. Finally, in step ST15 c 4 the call progress messagewith the relevant destination transport address is forwarded to thecalling multimedia terminal MTA, just like the call progress message instep ST15 a 12 for the distributed architecture in step 15 a.

As explained above with reference to the distributed architecture inFIG. 15 a and FIG. 15 d and with respect to the centralized architecturein FIG. 15 c and FIG. 15 d, during a call setup transport addresses ofsource and destination are exchanged between the two involved multimediaterminals MTA, MTB. When no switching resources are used, then thesource and destination transport addresses are merely the source anddestination transport addresses of the multimedia terminals MTA, MTB(see for example step ST15 d 4 and ST15 d 8 in FIG. 15 d). However, ifswitching resources are used on the calling and/or called multimediaterminal side (e.g. step ST15 d 2, step ST15 d 6), then the source ordestination address can be the own seized transport address. That is,when switching resources are seized or in use, a transport addresscorresponding to one of the PABX's own PSAPs can be selected and thus itis possible for the application layer connected to the MTA and/or MTB toselect the transport address that falls within a certain PSAP'stransport address range according to a series of rules (as explainedabove), e.g. for distributing the signaling load evenly amongst thePSAPs.

Fifth Embodiment (Supplementary Services)

As explained above, in addition to the discovery and registration ofmultimedia terminals MT in the extension space of the PABX, alsoswitching resources SW may be seized on the basis of exchangingsignaling information with the multimedia terminals MT during the callset-up. There is only no need to seize switching resources if anend-to-end network path can be set-up through the data network, the MT'scapabilities are the same or at least matched and the service level inthe data network is acceptable. Furthermore, during the call set-up—whenswitching resources SW must be used i.e. the data streams are at leastpartly routed through the switching means SW of the PABX—the controllercan also determine the transport address of the PSAP through which thesignaling and data streams are to be routed.

However, today the PABX networks provide a wide range of supplementaryservices to its normal telephony terminal users. Since the multimediaterminals MT have been made apart of the PABX extension space, it isalso possible to supply supplementary services from the applicationlayer of the PABX to the multimedia terminals MT. Thus, it is notnecessary to wait until the multimedia protocol being used describes allthese services for implementation in the data network. If thesupplementary services of the PABX are to be provided to the multimediaterminal, there must be a mechanism for “escaping” the multimediaprotocol to allow the implementation of any supplementary servicewithout regard to the multimedia protocol used.

Said mechanism has the advantage of being portable to differentmultimedia protocols, i.e the multimedia protocol being used in the PABXmight be replaced or a new multimedia protocol might be implemented andsupplementary services would still be implemented in a same way. Thatis, what is meant with “escaping” a multimedia protocol is that themultimedia protocol implementation in the multimedia controller MMC ofthe PABX is left. For doing so, the mechanism is composed of threephases which are explained hereinafter.

The first phase is the exchange of the transport addresses. Since thesupplementary services must be provided by the PABX, the multimediaterminal MT and the PABX exchange transport addresses which can be usedduring the call for signaling messages related to supplementaryservices. The supplementary services signaling might be carried out onconnection-orientated transport channels or a connectionless transportchannels. If a connection-oriented transport channel is used, it isenough if one of the sides, MT or PABX, delivers its transport addressto the opposite side. This allows the opposite side to set-up atransport connection to the received address which from the moment theconnection is ready can be used for bearing supplementary servicessignaling.

If a connectionless transport channel is used, both sides MT and PABXmust deliver their transport addresses to the opposite side. Both sideswill send messages related to the supplementary services to the othersides transport address.

For supplying the supplementary services the MT and the PABX must agreeon a type of transport channel to use. This is done by providing areference for connection-oriented and connectionless transport togetherwith the transport address for supplementary services. In case of adisagreement between the multimedia terminal's preference and the PABX'spreference in the type of transport channel, the PABX preference musthave presidence over the MR preference. That is, the selected transportchannel is dominated by the selection of the PABX.

The transport addresses for supplementary services signaling must beincluded in the registration messages of the multimedia protocol. Thisallows the implementation of non call-related supplementary services,since both sides MT and PABX know each other's transport address for thesupplementary services even before any call exists between them. Thatis, the exchange of the transport addresses is on the one hand necessaryto have the correct access port (transport address) through which thePABX will supply the supplementary services and on the other hand thePABX must have information (transport address) as to where thesupplementary services should be routed.

The fifth embodiment of the invention relates to claim 14. The transportaddress exchange algorithm is illustrated in FIG. 16. In FIG. 16 themost important aspect of the invention is the inclusion of transportaddresses for supplementary services in the respective signalingmessages.

In step ST161, ST161′ the multimedia terminal MT sends a registrationmessage to the PABX controller MMC, i.e. to its application layer ALMthrough the protocol handling layer PHLM. It indicates a type oftransport channel and the transport address of the multimedia terminalto which the supplementary services should be provided. The PABXcontroller MMC responds with a registration acknowledge message in stepST162′, ST162 indicating a type of transport channel and the transportaddress of the PABX through which supplementary services can be routed.The procedure in steps ST162 can be carried out repeatedly until thesame type of transport channel is agreed upon by the MT and the PABX. InFIG. 16 the information associated to the messages is that related tothe supplementary services channel only. Other information not reflectedin FIG. 16 may be included in the messages. For example, the messagesST161 and ST162 can also be combined with the registration messages ST13a 1, ST13 b 1 and the steps ST13 a 8, ST13 b 9 in FIGS. 13 a, 13 bduring the initial discovery and registration.

It should be noted that in the registration acknowledge message ST162the PABX's transport address for the supplementary services can beomitted if the PABX decided to use a connection-oriented transportchannel.

Furthermore, it should be noted that the transport address selected byeach side for supplementary services signaling must not be the same asany other transport address already selected or by some means reservedfor use by the multimedia protocol. Therefore, even if the supplementaryservices transport address registration is combined with the discoveryand registration procedures in FIGS. 13 a, 13 b, it must be ensured thatthe transport address used for the signaling for a call set-up is notthe same as the transport address for signaling relating tosupplementary services.

After agreeing upon the transport addresses through which thesupplementary services are respectively routed in the multimediaterminal MT and the PABX controller MMC, the second step is the openingof the agreed upon transport channel for the supplementary servicessignaling. Once the transport address exchange process is finished, thechannel for exchanging signaling related to supplementary services istherefore opened. For example, if a connectionless transport channel hasbeen agreed upon the channel is considered implicitly opened from themoment both sides MT and PABX controller have received the transportaddress for supplementary services signaling from the other side. If aconnection-oriented transport channel is agreed upon, the PABXcontroller must open a transport connection towards the transportaddress of the multimedia terminal MT called MT or calling Mt forsupplementary service at some moment after sending the registrationacknowledgement message in step ST162 (and preferably not before, sinceuntil the reception of the registration acknowledge message in themultimedia terminal, the multimedia terminal MT does not know anythingabout the selected transport channel).

That is, the AL must open a transport connection to any MT (called orcalling) with which it has been agreed to use a connection-orientedchannel for the supplementary services. It might happen that the channelto one of the MTs (called or calling) is a connectionless channel, andthe channel to the other MT is a connection-oriented channel.

After opening the supplementary services channel, the third step is theactual exchange of supplementary services signaling. That is, once thetransport channel is open, either implicitly or explicitly by the PABXcontroller, at any moment any side, the MT or the PABX, can send asignaling message related to a supplementary service through this set-upchannel. Two types of messages can be exchanged through this set-uptransport channel.

A first type are terminal-updating messages. These messages are sent bythe PABX and are received by the MT when supplementary servicessignaling is exchanged. These messages convey information related to thestate and visual indicators of the terminal. The information that can beconveyed by these messages include the following fields.

-   -   change of call state:    -   in this case the multimedia terminal MT changes its call state        (idle, occupied etc.) to the one which is conveyed in the        terminal update message received from the PABX.    -   display update:    -   the multimedia terminal MT shows the conveyed information on its        display.    -   user interface:    -   information related to the user interface that must be presented        by the multimedia terminal MT, depending on the call state.

The second type of messages are service request messages. These messagesare sent by the multimedia terminal MT and are received by the PABXcontroller. In these signaling messages service requests done by meansof user actions on elements of the multimedia terminal's user interfaceor spontaneously generated by the multimedia terminal MT are transportedto the PABX controller. These service requests can be performed by themultimedia terminal MT in two ways:

-   -   stimulous:    -   the services which is requested with the service request must be        identified by the PABX controller. In this case the PABX        controller identifies a supplementary service based on the        service request.    -   functional:    -   the multimedia terminal MT identifies the service which is to be        requested.

As explained above, since the multimedia terminal MT and the PABXexchange information regarding the transport channel and the transportaddress to be used for the supplementary services signaling,supplementary services can be provided from the PABX also to themultimedia terminal.

Furthermore, it should be understood that although the specific usage ofthe entities in FIGS. 5, 6, 7, 8, 9 is not described with reference tothe flow charts in FIGS. 16, 15 b, 15 a, 15 c, 15 d and FIG. 14, askilled person immediately realizes on the basis of the abovedescription that the physical signals, i.e. the data streams and thesignaling messages must be routed to the special transport address ofthe PSAP as shown in FIG. 6. It is actually the construction of thecontroller MMC with its layer structure which allows to make themultimedia terminal MT an extension of the PABX extension space, allow aregistration and discovery, the seizure of switching resources as wellas the usage of supplementary services from the PABX. In all cases, oncethe multimedia terminal MT is registered in the PABX controller theseizure or use of switching resources (including supplementaryresources) is made on the basis of interpreting signaling informationreceived from one or more connected multimedia terminals MT.

Sixth Embodiment (Network Resources Management)

As is well-known, in a multimedia data network network control messagescan be used for network resource management purposes. Such networkresource management can for example include the adaption of transferrates of an ongoing call or other call related adjustments. In a datanetwork the RSVP (Resource reservation Protocol) Protocol can be usedfor such network resource management purposes.

Since the multimedia terminals MT have been made to extensions of thenormal PABX extension space, according to a fifth embodiment of theinvention the multimedia controller MMC according to the invention alsoprovides the possibility to handle such network resource managementmessages if the multimedia protocol in the data network in use supportssuch messages for network resource management. Then, the applicationlayer device AL of the multimedia controller MMC can become a networkresources manager on behalf of the multimedia terminals MT for managingresources also in the data network. That is, the application layermanages packet switched network resources.

If the multimedia terminal wants to use some resources of the datanetwork, it must request the use of such resources at the PABXmultimedia controller MMN. These requests for resources must be made bythe multimedia terminal MT when either it starts a new call or it triesto increase the information transfer rate of an ongoing call. Likewise,when the multimedia terminal MT does not want the used resourcesanymore, it must inform the PABX controller of this fact. Therefore, themultimedia terminal MT must send a message to the PABX controller todrop a call or to decrease the information transfer rate of an ongoingcall.

In the PABX the multimedia controller MMC must upon reception of theserequest messages from the multimedia terminal MT execute an algorithmthat determine whether the requesting multimedia terminal MT has anauthorization for such an request. If the multimedia controllerdetermines that the multimedia terminal MT has such authorization, thenthe multimedia controller must interact with the network elements in theunderlying multimedia data network in order to seize or release packetsswitched resources as requested through the messages by the multimediaterminal MT.

In case one ore more of the network elements involved in the call werenot available to provide the requested resources the multimedia terminalMT must notify the PABX about this fact. The PABX controller must thennotify back to the multimedia terminal MT whether or not the requestcould be fulfilled. The PABX controller can use a series of checks inorder to decide whether to proceed with the multimedia terminal'srequest. These checks could include the following:

-   -   the multimedia terminal's O&M-assigned category allows it to        request more resources;    -   the multimedia terminal's O&M-assigned category allows it to        have the number of resources requested;    -   the class of call being transferred to by the resources request        deserves the requested resources; and    -   measurements on the data network status indicate if it is        possible to fulfill the resource request.

The sixth embodiment of the invention relates to claim 15. Thisprocedure is illustrated in FIG. 17. The most important aspect in theprocedure in FIG. 17 is the resource management algorithm. In stepST171, ST171′ the multimedia terminal MT sends a resource requestmessage including its identity, the requested resources and optionally acall reference if a call is already ongoing. The resource requestmessage in step ST171 is provided to the transport address of theapplication layer ALM of the PABX controller through the protocolhandling layer PHLM.

In step ST172 the first thing the PABX controller does is to fetch thecategory (terminal) profile by the identity. What is meant with categoryprofile is to check in the data structure of the multimedia terminal MTwhether the multimedia terminal MT is allowed to send such resourcemanagement messages, i.e. whether the multimedia protocol in use in amultimedia data network supports such messages. This can be more easilyunderstood by viewing the “Category Profile” as a “Terminal Profile”.The Terminal Profile is the information that contains, between otherdata, the operations and services this terminal is allowed to request.For instance, the Terminal Profile holds the information that stateswhether that terminal is allowed to do public calls.

For MTs, the Terminal Profile includes also information about whetherthe MT is allowed to have resources reserved in the data network forcertain types of calls, and if so, what is the maximum amount ofresources that are allowed to reserve for such call. The “check” as suchis not the Terminal (Category) Profile. The “check” is done in FIG. 17,ST173, and it is done by looking into the Terminal Profile at theinformation that states whether the terminal to which this profile isassociated has the right to have resources reserved.

If the profile does not allow the request in step ST173, then theresource management is rejected in step ST1710. If the profile allowsresource management massages in step ST173, then it is first decided instep ST174 whether the resource limit has been reached already. If theresource limit has already been reached, then of course no furtheradjustment can be made. Therefore the resource request is rejected againin step ST1710.

If there are still free resources which can be managed in step ST174,then in step ST175 the multimedia controller MMC fetches call data bycall reference. This is necessary to check whether the particular typeof call which is currently ongoing relates to a call class which allowsnetwork resource management requests. A call reference is used toidentify the call for which the network resources should be managed. Ifthe call class determined in step ST175 allows the network resourcemanagement request in step ST176, then the data network status ischecked in step ST177. If the status of the data network, i.e. itsunderlying multimedia protocol, allows adjustment of the networkresources, then in step ST179 network resources can be seized andreleased in accordance with the request made in the resource managementrequest message sent in step ST171. Therefore, a confirmation isdetermined in ST179′ and a resource confirmation message is returned instep ST1711′. A resource management acknowledgement message includingthe result of the resource adjustment, the resources and the callreference is sent back to the requesting multimedia terminal MT in stepST1711.

The method by which the PABX requests resources to the underlying datanetwork can be any new or already known method understandable by thenetwork elements of the data network and this seizure and release iscarried out in step ST179. The network resources request method is outof the scope of this invention but as an example, if the network elementsupport the aforementioned RSVP protocol, then the PABX controller cansend a RSVP request message to the called multimedia terminal MT. Thiscauses the network elements along the path to the called multimediaterminal MT to reserve resources for that call. This the approach chosenin H.323v2 and SIP.

Note that the aspect according to the fifth invention is the process bywhich the PABX controller decided whether network resources can orcannot be granted and if it can how much of them. For doing so, the PABXcontroller can process the received resource request messages and decidewhether or not further resources can be seized or must be released. Oncemore, the network resource management message in step ST171 is directedas a type of signaling message to a specific transport address of theapplication layer AL.

Therefore, in addition to the registration, discovery, basic call set-upand supplementary services used, the PABX controller according to theinvention can not only control the switching resources SW of the PABXnetwork for the call set-up but can also control the network resourcesof the data network to which the multimedia terminal MT is connected.All this is possible because the multimedia controller MMC according tothe invention has a layer structure which mirrors the layer structure ofthe multimedia data network. Therefore, it can issue the aforementionedRSVP message for the adjustment of the network elements which arelocated on the path to the multimedia terminal MT.

Seventh Embodiment (H.323 Gatekeeper/Gateway Integration)

With reference to FIGS. 18–21, an example case of the inventiondescribed in the previous sections will be explained. The use caseconsists of an H.323 Gatekeeper/Gateway application integrated in a PABXsystem. The following means are added to the PABX in order to enable theconnection of multimedia terminals MTs to it:

-   -   An Access PCB (APCB) which implements the whole Access Layer        means ALM as described above and shown in FIGS. 6, 7 and the        Media Gateway block MGM as described above and shown in FIG. 9        a;    -   The database DB (MTDB: multimedia data base) for holding the MT        specific information (MT's data structures) as described and        shown on the right side of FIG. 13 c;    -   A SW (switch) block (OMP) which implements the O&M Layer as        described above and shown in FIG. 11;    -   A SW (switch) block (LP) which implements the Protocol Handling        layer PHLM as described above and shown in FIG. 8, the Media        Controller block MCM as described above and shown in FIG. 9 a        and the Application layer ALM as described above and shown in        FIGS. 6, 7.

In FIG. 18 the architecture of the implementation is shown. As explainedabove, before being able to start using the PABX's switching resources,the multimedia terminals MTs must carry out a registration proceduresimilar to that described in the third embodiment and shown in FIGS. 13b, 13 c. Optionally, before the registration the multimedia terminals MTmay start a discovery procedure similar to that described in the thirdembodiment (automatic discovery) and shown in FIG. 13 a. In FIG. 19 themultimedia terminal MT on the left side performs a discovery as well asa registration processes, whilst the multimedia terminal MT on the rightside performs only the registration process. Once correctly registered,multimedia terminals MTs can make and receive calls.

In FIGS. 19, 20 the process of a MT to MT call setup is illustrated. Ascan be seen in the figure, for this call the result of the execution ofthe algorithm shown in FIG. 14 is that switching resources SW in thePABX are not seized, since after execution of said algorithm it can beassured that an end-to-end path through the underlying data network ispossible to be set-up a call between the two multimedia terminals MTs.Finally, the call is released according to FIG. 21.

Signals from AL to MTDB are for querying the MTDB contents.

Signals from AL to Network are for seizing or reserving data networkresources for the call that is about to be established.

The following description is a step-by-step description of thediscovery, registration, call setup and call release processes as wasabove described more generally for the individual procedures. However, aclear coherence exists between the embodiments described above and theexample case described here which is currently be regarded by theinventors as the best mode of the invention.

Discovery Process

Step ST231 is the H.323 counterpart of step ST13 a 1. The MT on the leftside sends a Discovery Request message GRQ with its identifiers(endpointAlias) and the transport address TA to which the DiscoveryConfirm or Discovery Reject message must be sent by the receivingapplication layer AL. This message is sent by said MT to the well-knowndiscovery multicast address defined in H.323, which is 224.0.1.41:1718in TCP/IP networks. Steps ST232/ST235 are the same ApplicationPrimitives as in steps ST13 a 1′/ST13 a 8′ in FIGS. 9 a, 9 b.

Steps ST233/ST234 represent a query to the MT database to check theidentities provided by the discovering MT against the MT databasecontents.

Step ST236 is the H.323 counterpart of ST13 a 8. The PHLM maps theApplication Primitive in step ST225 to a Gatekeeper Confirm message GCFwith the transport address TA to which the MT must send its furtherRegister Request message (rasAddress), and an identifier of theGatekeeper/PABX (gatekeeperId). This message is sent to the transportaddress TA received in step ST231 (rasAddress).

The transport address TA sent in step ST236 will have been chosen by theapplication AL between all those transport addresses TAs known by saidapplication layer AL, either corresponding to own PSAPs or foreignPSAPs, and can preferably be selected according to criteria mentioned inthe third embodiment.

Registration Process

Step ST239 is the H.323 counterpart of step ST13 b 1 and step ST161. Themultimedia terminal MT on the left side sends a Register Request messageRRQ with its identifiers, user and password (endpointAlias), its dynamictransport addresses TAs used for non call related signaling (rasAddress)and call related signaling (callSignalAddress), and the type andtransport address TA of the channel used for Supplementary Services(suppServChannel and SuppServAddress).

Steps ST2310/ST2315 are again the same Application Primitives as stepsST13 b 1′/ST13 b 9′ in FIG. 13 b. Steps ST2311/ST2312 represent a queryto the MT database to check the identities provided by the registeringmultimedia terminal MT against the MT database contents.

Steps ST2313/ST2314 represent the MT database update consequence of thereceived data related to the registering MT (rasAddress,callSignalAddress, suppServChannel and suppServAddress).

Step ST2316 is the H.323 counterpart of ST13 b 9 and ST162. The PHLMmaps the Application Primitive in step ST2315 to a Register Confirmmessage RCF with the Gatekeeper's transport address TA for call relatedsignaling (callSignalAddress), an identifier of the Gatekeeper/PABX(gatekeeperId), and the Gatekeeper's type of channel and transportaddress TA for Supplementary Services signaling (suppServChannel andsuppServAddress).

The transport addresses TAs sent in step ST2316 are preferably chosen bythe application layer AL between all those transport addresses TAs knownby said application layer AL, either corresponding to own PSAPs orforeign PSAPs, and selected according to criteria mentioned in the thirdembodiment.

Of course, the multimedia terminal MT on the right side in FIG. 19 alsocarries out a Registration process (steps ST237 and ST238). This processcauses a signaling exchange equal to that between steps ST2310 andST2315 which has been ommitted in sake of picture clarity.

Network Resource Management

Prior to starting a new call, the multimedia terminal MT requests theGatekeeper to reserve some network resources in the underlying datanetwork for holding said call. Step ST2317 is the H.323 counterpart ofstep ST171. The multimedia terminal MT on the left side sends anAdmission Request message ARQ with its identifiers (srcInfo), calledparty identifiers (destinationInfo), identifiers for the call(conferenceID and callIdentifier) and number of resources necessary(bandwidth). This message is sent to the transport address TA used fornon call related signaling of the Gatekeeper (rasAddress in step ST236).Steps ST2318/ST2321 indicate the same Application Primitives asST171′/ST1711′ in FIG. 17.

Steps ST2319/ST2320 represent an interaction between the applicationlayer AL and the underlying data network in order to negotiate seizingor reservation of resources in said data network. This interaction isdependent on the type of network (TCP/IP, AAL5/ATM etc.) and the way inwhich said network handles resources (RSVP, DiffServ, ATM QoS etc.).

Step ST2322 is the H.323 counterpart of step ST1711. The PHLM maps theApplication Primitive in step ST2321 to an Admission Confirm message ACFwith the actual number of resources that have been seized or reserved inthe data network (bandwidth). The called multimedia terminal MT alsogoes through this process when receiving the call setup notification.This is described in the Basic call setup section below.

Basic Call Setup

Step ST241 is the H.323 counterpart of step ST15 c 1. The multimediaterminal MT on the left side sends a call setup message (setup) with thecalled party E.164 number (calledPtyNum), identifiers for the call(conferenceID and callIdentifier) which must match those which themultimedia terminal MT sent in step ST2217, and the transport address TAused by said multimedia terminal MT to receive packets bearingmultimedia information (MHLAddress). This transport address TA has thesame meaning as the <MT A's Tr. Addr.> field in step ST15 c 1.

Steps ST242/ST243 are the Application Primitives corresponding to thecall setup message (setup), which were not shown in FIG. 15 c forclarity.

Step ST244 is the H.323 counterpart of step ST15 c 2. The MHLAddress instep ST244 might be that sent by the calling MT in ST241, or a differentone selected by the application layer AL during execution of the methodin FIG. 15 d. This address has the same meaning as the <Source Tr.Addr.> field in step ST15 c 2.

The signaling between step ST245 and step ST2410 is similar to thatbetween step ST2217 and step ST2222. The called multimedia terminal MTalso requests from its Gatekeeper the number of underlying data networkresources which it is going to need for the call (it might be that adifferent number of resources is needed in each direction, for instanceif the calling multimedia terminal MT sends only an audio stream whilethe called multimedia terminal MT sends both an audio and a videostream).

Step ST2411 is the H.323 counterpart of step ST15 c 3. The multimediaterminal MT on the right side sends a call connection message (connect)with identifiers for the call (conferenceID and callIdentifier) and thetransport address TA which this MT wishes to use for receiving packetsbearing multimedia information (MHLAddress). This transport address TAhas the same meaning as <MT B's Tr. Addr.> field in steps ST15 c 3.

Steps ST2412/ST2413 are the Application Primitives corresponding to thecall connect message (connect), which were not shown in FIG. 15 c forclarity. Step ST2414 is the H.323 counterpart of step ST15 c 4. The PHLMmaps the CALLANS.ind Primitive to a call connect message (connect) withthe identifiers for the call (conferenceID and callIdentifier) and thetransport address TA to where the calling multimedia terminal MT mustsend its packets bearing multimedia information.

The MHLAddress in step ST2414 might be that sent by the calledmultimedia terminal MT in step ST2411, or a different one selected bythe AL during execution of algorithm in FIG. 15 d. This address has thesame meaning as the <Dest. Tr. Addr.> field in step ST15 c 4.

As can be seen from the above description, now both calling and calledmultimedia terminal MT know the transport addresses TAs to which theymust sent their packets bearing multimedia information. In this usecase, MHLAddress fields sent by multimedia terminals MTs have not beenmodified by the application layer AL since said application layer AL hasfound that en end-to-end signaling path can be setup between calling andcalled multimedia MT through the underlying data network. Therefore thetransport addresses TAs which both multimedia terminals MTs must use forsending multimedia streams are each respective MT's transport addressTA, and the multimedia streams flow directly between the MTs withouttraversing through the PABX's switch, as can be seen in step ST2415.

Call Release

Signaling between steps ST251 and ST254 is the standard H.323 signalingfor releasing a call. The calling multimedia terminal MT (the calledmultimedia terminal MT can also release the call) sends a call releasemessage (releaseComplete) via the mapping and the correspondingApplication Primitives through the to the application layer AL to arriveat the the called multimedia terminal MT. The releasing multimediaterminal MT identifies the call to release by including call identifiers(conferenceID and callIdentifier) in the releaseComplete message.Signaling between steps ST255 and ST2510, and between steps ST2511 andST2516 have a function opposite to that of signaling between stepsST2317 and ST2322, and between steps ST245 and ST2410. Both multimediaterminals MTs notify their Gatekeepers (in this case both MTs are usingthe same Gatekeeper) that the data network resources used for the callthat is being terminated can be released.

It should be noted that in the description of the above use example alldenotations in steps between the multimedia terminals and the respectivelayers PHLM and AL designate messages containing one or more parameterswhilst the steps between the layers e.g. PHLM and AL in capital lettersdesignate the exchange of the primitives as already explained above withreference to FIGS. 6–9. This also applies to the figures with the otherflow charts e.g. in FIGS. 13 a, 13 b, 14, 15 a, 15 c, 16, 17.

INDUSTRIAL APPLICABILITY

As explained above, rather than using a gateway the present inventionincorporates in a circuit switched network a multimedia controller whichallows to handle the multimedia terminal MT connected to the datanetwork connected to the circuit switched network to be treated justlike any other normal telephony terminal extension. For doing so, thecontroller mirrors at least part of the protocol layer structurenormally used in the data network. If a new data network having adifferent type or standard of multimedia protocol is connected to thePABX then only specific procedures in the individual layers of thecontroller need to be updated/replaced.

For call set-up requests from multimedia terminals MT which are now partof the extension space of the PABX the multimedia controller receivessignaling messages in the multimedia data format, decodes thesesignaling messages and controlls the use of switching resources of thePABX in accordance with the content of the signaling messages.

By exchanging transport addresses with the multimedia terminal MT thePABX multimedia controller can perform distribution of the signalingload and of the call-related media information between a number ofdifferent physical service access points PSAP which are part of thephysical and data link sublayer.

The multimedia controller can also provide supplementary services of thePABX network to the multimedia terminal MT when a corresponding exchangeof signaling messages is performed between MT and multimedia controller.

Finally, if the protocol used in the data network supports this, alsonetwork resource management functions can be carried out by the PABXmultimedia controller.

As explained above with reference to the layer structure of theinventive PABX multimedia controller, whenever a new protocol is used inthe data network, it is only necessary to exchange certain algorithms inthe layer structure without replacing the complete controller. It isalso possible that several algorithms coexist in each of the layers suchthat even when a new multimedia protocol data network is connected anautomatic selection of the appropriate algorithm/sublayer is performed.

Therefore, it should be understood that the present invention is by nomeans restricted to the usage of specific protocols like IPX, H.323,PCP/IP etc. Quite to the contrary, on the basis of the above teachingsvarious modifications and variations of the present invention can becarried out on the basis of the teachings disclosed herein. Inparticular, the invention can comprise embodiments consisting offeatures which have been separately described in the claims and/or inthe description. Furthermore, it should be noted that what has beendescribed above is only what the inventors presently conceive as thebest mode of the invention and further advantageous embodiments may bedevised on the teachings diclosed herein. Therefore, the scope of theinvention is not restricted to the description.

Furthermore, reference numerals in the claims only serve clarificationpurposes and are by no means intended to be restricting the scope ofthese claims.

1. A circuit switched Private Branch Exchange System (PABX) comprising switching resources (SW) for providing communications between first subscriber stations (TT) belonging to the circuit switched extension realm of said system, characterized by: a multimedia controller multimedia controller (MMC) adapted to control said switching resources (SW) for providing communications between a first subscriber station (TT) and a second subscriber station (MT) of a Multimedia Data Network (MMN), or between second subscriber stations (MTs), the multimedia controller (MMC) comprising: a) Access Layer means (ALM), containing a plurality of physical and data link sub-layers (PDLSUB) and a Network and transport sub-layers (NTSUB), for connecting the multimedia controller (MMC) with the data network where the second subscribers are connected; b) Protocol Handling Layer means (PHLM), for processing the multimedia protocol messages that are exchanged with a second subscriber related to a communication that involves, at least, a second subscriber; c) Media Handling Layer means (MHL), for handling processes related to media exchange with a second subscriber related to a communication that involves, at least, a second subscriber; d1) Operation and Maintenance Layer means (OML), for setting and storing a data structure related to each admissible second subscriber, said data structure comprising for each admissible second subscriber a directory number belonging to the PABX's number space, and one data or any combination thereof among: network identification and addressing data, multimedia capabilities data, security information data, d2) said Operation and Maintenance Layer means (OML) comprising means for setting (ST121–ST125) in a database (DB) the relationship between a multimedia terminal's data structure and said directory number; e1) Application layer means (AL) for controlling the underlying layers Access Layer means (ALM), Protocol Handling Layer means (PHLM) and Media Handling Layer means (MHL), the AL interfacing with control blocks in the PABX (COL), and comprising means for processing basic services (BSM) for supplementary services (SSM), and e2) said Application Layer means (AL) comprising means for receiving a protocol message from one of said first or second subscriber stations in the form of a primitive to interpret said primitive, to perform control of said switching resources (SW).
 2. A method for integrating in the extension space of a system as described in claim 1 at least one second subscriber station (MT), the method comprising the steps of (ST121–ST125); initiating a new directory number for said second subscriber, initiating for said second subscriber a data structure comprising one data or any combination thereof among: network identification and addressing data, multimedia capabilities data, security information data, storing said data structure in a database (DB), creating a relationship between said new directory number and said data structure.
 3. A method according to claim 2 further comprising the following steps for the discovery phase of a second subscriber station (MT) in a system as described in claim 1: in said second subscriber station (MT), sending (ST13 a 1, ST13 a 1′) a discovery message including an identity information of said second subscriber station (MT) to a fixed transport address of a protocol handling layer means (PHLM) of the multimedia controller multimedia controller (MMC); and in said multimedia controller multimedia controller (MMC), checking (ST13 a 2) the identity information against the data structures in said data base (DB) to find a corresponding directory number and, if a match is found, sending (ST13 a 8, ST13 a 8′) back to said second subscriber station (MT) a confirmation message including a transport address of the protocol handling layer means (PHLM) through which the protocol handling layer means (PHLM) can receive registration admission and status (RAS) messages.
 4. A method according to any of claim 3 characterized in that said multimedia controller (MMC) determines the transport address for each discovering or registering second subscriber station (MT) depending on the signaling load of several physical signal access ports (PSAP) of the plurality of physical and data link sub-layer devices (PDLSUB) in said multimedia controller (MMC).
 5. A method according to claim 2 further comprising the following steps for the registration phase of a second subscriber station (MT) in a system as described in claim 1: in said second subscriber station (MT), sending (ST13 b 1, ST13 b 1′) a registration request message (REGISTER) including at least an identity information of said second subscriber station (MT) to a transport address of a protocol handling layer means (PHLM) of the multimedia controller (MMC); and in said multimedia controller (MMC), checking (ST13 b 2) the identity information against the data structures in said data base (DB) and, if a match is found, sending (ST13 b 9) back to said second subscriber station (MT) a registration confirmation message (REGISTER ACK) including a transport address of the protocol handling layer means (PHLM) through which the protocol handling layer means (PHLM) can receive call signalling messages.
 6. A method according to claim 5 characterized in that, in said registration request message and said registration confirmation message, said second subscriber station (MT) and the multimedia controller (MMC) exchange transport addresses and the type of transport channel used for exchanging signaling related to supplementary services.
 7. A method according to any of claim 2 further comprising the following steps for providing communications in a system as described in claim 1 between a second subscriber station (MT) and a communication counterpart first subscriber station (TT) or second subscriber station (MT): in said multimedia controller (MMC), receiving a protocol message requesting a call establishment (CALL SETUP) from a calling subscriber station (MT,TT), said protocol message comprising, at least, an identification for a counterpart called subscriber station (MT,TT) and a transport address where said calling subscriber station can receive media data stream related to said data, in said multimedia controller (MMC), determining if said call establishment message comes from a first subscriber station (TT) or from a second subscriber station (MT), in said multimedia controller (MMC), determining if said called subscriber station is a first subscriber station (TT) or a second subscriber station (MT), in said multimedia controller (MMC), determining if the switching resources (SW) in said system shall be used for said call, from said multimedia controller (MMC), sending a protocol message requesting a call establishment (CALL SETUP) to said called subscriber station (MT, TT), said message comprising a transport address where said called subscriber station shall send media data stream related to said call, in said multimedia controller (MMC), receiving a protocol message indicating a call progress for said call establishment request (CALL PROGRESS) from said called subscriber station said message comprising a transport address where said called subscriber station can receive media data stream related to said call, and from said multimedia controller (MMC), sending a protocol message indicating a call progress for said call establishment request (CALL PROGRESS) to said calling subscriber station said message comprising a transport address where said calling subscriber station shall send media data stream related to said call.
 8. A method according to claim 7 characterized in that said multimedia controller (MMC) determines the usage of said switching resources (SW) on the basis of checking (ST142) whether an end-to-end network path is possible (ST142) between the calling and called subscriber station, by checking their respective terminal's coding schemes (ST145) and by checking the data network service level (ST146).
 9. A method according to claim 7, characterized in that, when switching resources in said system (SW) are used, the multimedia controller (MMC) determines the transport address of one of several physical service access points (PSAP) in order to distribute call-related media information amongst several physical service access points (PSAP).
 10. A method according to any of claim 7 further comprising the following steps for managing the network resources used by a second subscriber station (MT) related to a call in which said second subscriber station is involved: in said second subscriber station (MT), sending a data network resource management request message to the multimedia controller (MMC), in said multimedia controller (MMC), determining whether a data network resource management is allowed based on the category profile (ST173), the resource availability (ST174), the call class (ST176) and the data network status (ST178), and in said multimedia controller (MMC) issuing data network resource management messages to the data network in accordance with the resource request made in the data network resource management request message issued from the second subscriber station (MT). 